ABI.rst: Update struct layout discussion.
ABI.rst: Update struct layout discussion.

Describe the "Universal" layout algorithm in full, and update the examples to use packed structs, following the recent IRGen changes.

Swift SVN r9143

amraboelela/swift,zisko/swift,djwbrown/swift,SwiftAndroid/swift,jmgc/swift,gmilos/swift,deyton/swift,kperryua/swift,jtbandes/swift,deyton/swift,kusl/swift,felix91gr/swift,amraboelela/swift,sschiau/swift,ben-ng/swift,xwu/swift,kperryua/swift,shahmishal/swift,karwa/swift,cbrentharris/swift,slavapestov/swift,hughbe/swift,emilstahl/swift,slavapestov/swift,dduan/swift,ben-ng/swift,frootloops/swift,nathawes/swift,deyton/swift,MukeshKumarS/Swift,shajrawi/swift,LeoShimonaka/swift,CodaFi/swift,nathawes/swift,tinysun212/swift-windows,jckarter/swift,sschiau/swift,jmgc/swift,alblue/swift,kstaring/swift,brentdax/swift,sdulal/swift,Ivacker/swift,gribozavr/swift,allevato/swift,codestergit/swift,mightydeveloper/swift,gmilos/swift,karwa/swift,apple/swift,KrishMunot/swift,IngmarStein/swift,glessard/swift,manavgabhawala/swift,xedin/swift,shahmishal/swift,kstaring/swift,OscarSwanros/swift,modocache/swift,SwiftAndroid/swift,glessard/swift,stephentyrone/swift,kusl/swift,MukeshKumarS/Swift,kstaring/swift,tardieu/swift,austinzheng/swift,tardieu/swift,kusl/swift,ken0nek/swift,austinzheng/swift,lorentey/swift,tardieu/swift,frootloops/swift,practicalswift/swift,tjw/swift,mightydeveloper/swift,kperryua/swift,CodaFi/swift,glessard/swift,Ivacker/swift,sdulal/swift,parkera/swift,johnno1962d/swift,uasys/swift,milseman/swift,swiftix/swift,JaSpa/swift,jckarter/swift,LeoShimonaka/swift,OscarSwanros/swift,stephentyrone/swift,gribozavr/swift,Jnosh/swift,sschiau/swift,felix91gr/swift,deyton/swift,slavapestov/swift,hughbe/swift,hughbe/swift,sdulal/swift,glessard/swift,alblue/swift,atrick/swift,apple/swift,djwbrown/swift,dduan/swift,arvedviehweger/swift,KrishMunot/swift,Ivacker/swift,CodaFi/swift,LeoShimonaka/swift,milseman/swift,felix91gr/swift,manavgabhawala/swift,hughbe/swift,modocache/swift,manavgabhawala/swift,MukeshKumarS/Swift,tinysun212/swift-windows,harlanhaskins/swift,benlangmuir/swift,gregomni/swift,xwu/swift,airspeedswift/swift,dreamsxin/swift,calebd/swift,modocache/swift,roambotics/swift,shahmishal/swift,devincoughlin/swift,jckarter/swift,CodaFi/swift,milseman/swift,roambotics/swift,OscarSwanros/swift,uasys/swift,tinysun212/swift-windows,sschiau/swift,xedin/swift,arvedviehweger/swift,milseman/swift,ken0nek/swift,hooman/swift,jopamer/swift,zisko/swift,gribozavr/swift,therealbnut/swift,zisko/swift,airspeedswift/swift,harlanhaskins/swift,gottesmm/swift,austinzheng/swift,OscarSwanros/swift,khizkhiz/swift,gottesmm/swift,manavgabhawala/swift,lorentey/swift,huonw/swift,gregomni/swift,jtbandes/swift,jckarter/swift,johnno1962d/swift,calebd/swift,Ivacker/swift,natecook1000/swift,ahoppen/swift,danielmartin/swift,gribozavr/swift,ken0nek/swift,adrfer/swift,xedin/swift,uasys/swift,JGiola/swift,hooman/swift,arvedviehweger/swift,shahmishal/swift,IngmarStein/swift,kstaring/swift,jopamer/swift,milseman/swift,LeoShimonaka/swift,bitjammer/swift,codestergit/swift,kusl/swift,adrfer/swift,rudkx/swift,benlangmuir/swift,manavgabhawala/swift,jopamer/swift,tjw/swift,slavapestov/swift,swiftix/swift.old,russbishop/swift,gmilos/swift,austinzheng/swift,danielmartin/swift,jtbandes/swift,natecook1000/swift,glessard/swift,OscarSwanros/swift,tardieu/swift,dduan/swift,austinzheng/swift,sdulal/swift,xwu/swift,sdulal/swift,jmgc/swift,aschwaighofer/swift,sschiau/swift,airspeedswift/swift,jckarter/swift,austinzheng/swift,cbrentharris/swift,devincoughlin/swift,rudkx/swift,parkera/swift,brentdax/swift,harlanhaskins/swift,brentdax/swift,allevato/swift,tjw/swift,huonw/swift,therealbnut/swift,Jnosh/swift,roambotics/swift,harlanhaskins/swift,russbishop/swift,gottesmm/swift,KrishMunot/swift,emilstahl/swift,swiftix/swift,allevato/swift,manavgabhawala/swift,hooman/swift,johnno1962d/swift,CodaFi/swift,mightydeveloper/swift,jopamer/swift,harlanhaskins/swift,shahmishal/swift,shahmishal/swift,huonw/swift,ken0nek/swift,dduan/swift,mightydeveloper/swift,calebd/swift,roambotics/swift,natecook1000/swift,emilstahl/swift,stephentyrone/swift,SwiftAndroid/swift,shajrawi/swift,khizkhiz/swift,calebd/swift,JGiola/swift,tinysun212/swift-windows,dduan/swift,MukeshKumarS/Swift,zisko/swift,codestergit/swift,Ivacker/swift,therealbnut/swift,khizkhiz/swift,calebd/swift,aschwaighofer/swift,LeoShimonaka/swift,shajrawi/swift,emilstahl/swift,huonw/swift,tjw/swift,JaSpa/swift,swiftix/swift.old,swiftix/swift.old,alblue/swift,codestergit/swift,xedin/swift,jtbandes/swift,devincoughlin/swift,aschwaighofer/swift,bitjammer/swift,return/swift,JaSpa/swift,benlangmuir/swift,nathawes/swift,manavgabhawala/swift,frootloops/swift,ben-ng/swift,djwbrown/swift,JGiola/swift,frootloops/swift,therealbnut/swift,huonw/swift,LeoShimonaka/swift,cbrentharris/swift,shajrawi/swift,shahmishal/swift,swiftix/swift.old,jtbandes/swift,CodaFi/swift,shajrawi/swift,kusl/swift,xedin/swift,natecook1000/swift,hooman/swift,kstaring/swift,JaSpa/swift,KrishMunot/swift,kusl/swift,shahmishal/swift,johnno1962d/swift,kentya6/swift,bitjammer/swift,tkremenek/swift,xwu/swift,ahoppen/swift,slavapestov/swift,devincoughlin/swift,SwiftAndroid/swift,devincoughlin/swift,xedin/swift,lorentey/swift,russbishop/swift,bitjammer/swift,allevato/swift,uasys/swift,tardieu/swift,atrick/swift,ken0nek/swift,arvedviehweger/swift,LeoShimonaka/swift,cbrentharris/swift,tjw/swift,gottesmm/swift,jmgc/swift,airspeedswift/swift,adrfer/swift,hooman/swift,russbishop/swift,return/swift,calebd/swift,felix91gr/swift,stephentyrone/swift,ahoppen/swift,return/swift,tkremenek/swift,adrfer/swift,johnno1962d/swift,cbrentharris/swift,rudkx/swift,ken0nek/swift,sdulal/swift,lorentey/swift,tkremenek/swift,milseman/swift,tkremenek/swift,nathawes/swift,stephentyrone/swift,djwbrown/swift,swiftix/swift.old,return/swift,KrishMunot/swift,cbrentharris/swift,MukeshKumarS/Swift,tardieu/swift,modocache/swift,amraboelela/swift,gottesmm/swift,Jnosh/swift,devincoughlin/swift,lorentey/swift,Ivacker/swift,roambotics/swift,dduan/swift,rudkx/swift,khizkhiz/swift,kusl/swift,kentya6/swift,hooman/swift,Jnosh/swift,swiftix/swift,parkera/swift,modocache/swift,mightydeveloper/swift,deyton/swift,mightydeveloper/swift,atrick/swift,zisko/swift,aschwaighofer/swift,emilstahl/swift,allevato/swift,JaSpa/swift,brentdax/swift,codestergit/swift,tkremenek/swift,glessard/swift,kentya6/swift,IngmarStein/swift,natecook1000/swift,OscarSwanros/swift,bitjammer/swift,stephentyrone/swift,parkera/swift,gribozavr/swift,rudkx/swift,dreamsxin/swift,nathawes/swift,emilstahl/swift,sdulal/swift,swiftix/swift,xwu/swift,karwa/swift,practicalswift/swift,frootloops/swift,alblue/swift,hughbe/swift,return/swift,xwu/swift,SwiftAndroid/swift,JaSpa/swift,codestergit/swift,IngmarStein/swift,ahoppen/swift,slavapestov/swift,aschwaighofer/swift,kperryua/swift,therealbnut/swift,CodaFi/swift,adrfer/swift,gribozavr/swift,danielmartin/swift,hooman/swift,OscarSwanros/swift,alblue/swift,sschiau/swift,kusl/swift,nathawes/swift,swiftix/swift,austinzheng/swift,karwa/swift,tkremenek/swift,aschwaighofer/swift,emilstahl/swift,nathawes/swift,zisko/swift,gmilos/swift,airspeedswift/swift,hughbe/swift,return/swift,emilstahl/swift,tinysun212/swift-windows,modocache/swift,jmgc/swift,frootloops/swift,kentya6/swift,ben-ng/swift,benlangmuir/swift,brentdax/swift,SwiftAndroid/swift,aschwaighofer/swift,IngmarStein/swift,uasys/swift,xwu/swift,airspeedswift/swift,jopamer/swift,ben-ng/swift,sschiau/swift,jckarter/swift,milseman/swift,gribozavr/swift,tkremenek/swift,gottesmm/swift,arvedviehweger/swift,ben-ng/swift,kentya6/swift,alblue/swift,Ivacker/swift,codestergit/swift,kentya6/swift,atrick/swift,danielmartin/swift,djwbrown/swift,danielmartin/swift,therealbnut/swift,kperryua/swift,brentdax/swift,karwa/swift,ahoppen/swift,apple/swift,jopamer/swift,cbrentharris/swift,huonw/swift,parkera/swift,karwa/swift,swiftix/swift,adrfer/swift,stephentyrone/swift,JaSpa/swift,kstaring/swift,Jnosh/swift,brentdax/swift,return/swift,jmgc/swift,shajrawi/swift,uasys/swift,Jnosh/swift,Ivacker/swift,gottesmm/swift,deyton/swift,johnno1962d/swift,jtbandes/swift,airspeedswift/swift,practicalswift/swift,kperryua/swift,practicalswift/swift,khizkhiz/swift,uasys/swift,practicalswift/swift,KrishMunot/swift,tjw/swift,kstaring/swift,bitjammer/swift,shajrawi/swift,apple/swift,frootloops/swift,sschiau/swift,roambotics/swift,xedin/swift,jopamer/swift,practicalswift/swift,swiftix/swift.old,ben-ng/swift,atrick/swift,adrfer/swift,russbishop/swift,swiftix/swift.old,deyton/swift,russbishop/swift,jtbandes/swift,IngmarStein/swift,arvedviehweger/swift,kentya6/swift,zisko/swift,Jnosh/swift,karwa/swift,MukeshKumarS/Swift,IngmarStein/swift,harlanhaskins/swift,benlangmuir/swift,atrick/swift,practicalswift/swift,parkera/swift,karwa/swift,kperryua/swift,lorentey/swift,LeoShimonaka/swift,JGiola/swift,gribozavr/swift,gmilos/swift,tjw/swift,natecook1000/swift,shajrawi/swift,felix91gr/swift,JGiola/swift,ken0nek/swift,khizkhiz/swift,harlanhaskins/swift,swiftix/swift,lorentey/swift,gregomni/swift,djwbrown/swift,allevato/swift,practicalswift/swift,calebd/swift,natecook1000/swift,arvedviehweger/swift,hughbe/swift,tinysun212/swift-windows,danielmartin/swift,bitjammer/swift,amraboelela/swift,swiftix/swift.old,allevato/swift,devincoughlin/swift,kentya6/swift,therealbnut/swift,gmilos/swift,amraboelela/swift,tinysun212/swift-windows,dduan/swift,KrishMunot/swift,mightydeveloper/swift,danielmartin/swift,slavapestov/swift,amraboelela/swift,SwiftAndroid/swift,ahoppen/swift,amraboelela/swift,jmgc/swift,khizkhiz/swift,benlangmuir/swift,johnno1962d/swift,cbrentharris/swift,parkera/swift,alblue/swift,djwbrown/swift,russbishop/swift,MukeshKumarS/Swift,mightydeveloper/swift,xedin/swift,JGiola/swift,tardieu/swift,gregomni/swift,gmilos/swift,devincoughlin/swift,gregomni/swift,huonw/swift,rudkx/swift,lorentey/swift,felix91gr/swift,felix91gr/swift,jckarter/swift,parkera/swift,apple/swift,apple/swift,modocache/swift,sdulal/swift,gregomni/swift