Improved the description of loadable and address-only types
Improved the description of loadable and address-only types

Added a missing requirement that loadable types must be loaded and
stored in terms of their parts. Added some examples of loadable and
address-only types that are not expressible in Swift today but help
illustrate the concepts.

benlangmuir/swift,hooman/swift,apple/swift,xwu/swift,harlanhaskins/swift,rudkx/swift,glessard/swift,nathawes/swift,roambotics/swift,jckarter/swift,JGiola/swift,harlanhaskins/swift,jckarter/swift,allevato/swift,glessard/swift,tkremenek/swift,airspeedswift/swift,airspeedswift/swift,CodaFi/swift,ahoppen/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,allevato/swift,harlanhaskins/swift,parkera/swift,glessard/swift,benlangmuir/swift,atrick/swift,stephentyrone/swift,tkremenek/swift,xwu/swift,airspeedswift/swift,harlanhaskins/swift,CodaFi/swift,jmgc/swift,JGiola/swift,tkremenek/swift,jckarter/swift,stephentyrone/swift,harlanhaskins/swift,CodaFi/swift,glessard/swift,airspeedswift/swift,rudkx/swift,rudkx/swift,JGiola/swift,allevato/swift,CodaFi/swift,gregomni/swift,ahoppen/swift,CodaFi/swift,roambotics/swift,parkera/swift,rudkx/swift,tkremenek/swift,allevato/swift,apple/swift,parkera/swift,stephentyrone/swift,atrick/swift,gregomni/swift,tkremenek/swift,gregomni/swift,roambotics/swift,airspeedswift/swift,hooman/swift,JGiola/swift,nathawes/swift,xwu/swift,gregomni/swift,ahoppen/swift,harlanhaskins/swift,hooman/swift,jckarter/swift,apple/swift,jmgc/swift,xwu/swift,parkera/swift,xwu/swift,benlangmuir/swift,stephentyrone/swift,glessard/swift,xwu/swift,apple/swift,jmgc/swift,airspeedswift/swift,CodaFi/swift,ahoppen/swift,benlangmuir/swift,jckarter/swift,benlangmuir/swift,hooman/swift,hooman/swift,tkremenek/swift,parkera/swift,harlanhaskins/swift,atrick/swift,tkremenek/swift,nathawes/swift,nathawes/swift,jckarter/swift,atrick/swift,jmgc/swift,parkera/swift,CodaFi/swift,hooman/swift,atrick/swift,hooman/swift,nathawes/swift,glessard/swift,jmgc/swift,JGiola/swift,rudkx/swift,jmgc/swift,ahoppen/swift,parkera/swift,nathawes/swift,atrick/swift,roambotics/swift,apple/swift,allevato/swift,airspeedswift/swift,stephentyrone/swift,gregomni/swift,jckarter/swift,apple/swift,stephentyrone/swift,nathawes/swift,allevato/swift,ahoppen/swift,rudkx/swift,allevato/swift,parkera/swift,xwu/swift,jmgc/swift,JGiola/swift,stephentyrone/swift,roambotics/swift