extra: Add getter methods to extra::rational::Ratio
extra: Add getter methods to extra::rational::Ratio

After merging 0ada7c7, user code have not been able to access to `Ratio`'s numerator and denominator fields.
In some algorithms, it is needed to get an rational number's numerator or denominator, but keeping these fields private is necessary for guaranteeing that `Ratio` numbers are irreducible.
So, I added the getter methods `numer()` and `denom()`.

As a bonus, this commit adds utility methods relating to the ratio-integer conversion.

AerialX/rust,Ryman/rust,pythonesque/rust,miniupnp/rust,SiegeLord/rust,AerialX/rust-rt-minimal,hauleth/rust,quornian/rust,zachwick/rust,mvdnes/rust,carols10cents/rust,hauleth/rust,servo/rust,dwillmer/rust,retep998/rand,stepancheg/rust-ide-rust,dwillmer/rust,rohitjoshi/rust,aneeshusa/rust,KokaKiwi/rust,AerialX/rust-rt-minimal,ruud-v-a/rust,barosl/rust,bombless/rust,jroesch/rust,barosl/rust,jashank/rust,dinfuehr/rust,ruud-v-a/rust,jroesch/rust,servo/rust,stepancheg/rust-ide-rust,pelmers/rust,defuz/rust,dinfuehr/rust,gifnksm/rust,pelmers/rust,TheNeikos/rust,nwin/rust,AerialX/rust-rt-minimal,jbclements/rust,kwantam/rust,GBGamer/rust,avdi/rust,aturon/rust,ktossell/rust,shepmaster/rand,waynenilsen/rand,pshc/rust,jroesch/rust,SiegeLord/rust,kimroen/rust,michaelballantyne/rust-gpu,zubron/rust,bombless/rust-docs-chinese,sae-bom/rust,pshc/rust,ruud-v-a/rust,l0kod/rust,omasanori/rust,servo/rust,pythonesque/rust,nham/rust,seanrivera/rust,omasanori/rust,GBGamer/rust,robertg/rust,Ryman/rust,mihneadb/rust,ktossell/rust,aidancully/rust,andars/rust,GBGamer/rust,aturon/rust,philyoon/rust,philyoon/rust,andars/rust,aepsil0n/rust,mdinger/rust,andars/rust,miniupnp/rust,mvdnes/rust,victorvde/rust,nwin/rust,vhbit/rust,GrahamDennis/rand,untitaker/rust,sae-bom/rust,emk/rust,stepancheg/rust-ide-rust,Ryman/rust,nwin/rust,seanrivera/rust,l0kod/rust,KokaKiwi/rust,krzysz00/rust,krzysz00/rust,graydon/rust,aturon/rust,jashank/rust,AerialX/rust-rt-minimal,omasanori/rust,mdinger/rust,kimroen/rust,pshc/rust,bhickey/rand,cllns/rust,victorvde/rust,pelmers/rust,zaeleus/rust,defuz/rust,Ryman/rust,mihneadb/rust,avdi/rust,rprichard/rust,nwin/rust,rprichard/rust,fabricedesre/rust,erickt/rust,P1start/rust,servo/rust,robertg/rust,emk/rust,0x73/rust,reem/rust,ktossell/rust,mitsuhiko/rust,dwillmer/rust,zubron/rust,mihneadb/rust,stepancheg/rust-ide-rust,Ryman/rust,jashank/rust,rprichard/rust,robertg/rust,jbclements/rust,zubron/rust,defuz/rust,emk/rust,dwillmer/rust,krzysz00/rust,zaeleus/rust,nham/rust,reem/rust,avdi/rust,sae-bom/rust,cllns/rust,zaeleus/rust,nwin/rust,bombless/rust,jbclements/rust,ebfull/rust,hauleth/rust,TheNeikos/rust,gifnksm/rust,mvdnes/rust,ejjeong/rust,fabricedesre/rust,0x73/rust,GBGamer/rust,dinfuehr/rust,aturon/rust,nham/rust,ebfull/rust,ebfull/rand,ebfull/rust,pythonesque/rust,nham/rust,zaeleus/rust,zachwick/rust,krzysz00/rust,zubron/rust,SiegeLord/rust,aturon/rust,kimroen/rust,SiegeLord/rust,mitsuhiko/rust,SiegeLord/rust,mahkoh/rust,vhbit/rust,jroesch/rust,servo/rust,krzysz00/rust,nwin/rust,michaelballantyne/rust-gpu,gifnksm/rust,andars/rust,kimroen/rust,P1start/rust,jbclements/rust,erickt/rust,Ryman/rust,quornian/rust,michaelballantyne/rust-gpu,pczarn/rust,zachwick/rust,AerialX/rust,emk/rust,victorvde/rust,carols10cents/rust,KokaKiwi/rust,l0kod/rust,dwillmer/rust,zubron/rust,ktossell/rust,TheNeikos/rust,pelmers/rust,krzysz00/rust,GBGamer/rust,jashank/rust,aneeshusa/rust,omasanori/rust,avdi/rust,P1start/rust,aneeshusa/rust,erickt/rust,fabricedesre/rust,ktossell/rust,arthurprs/rand,avdi/rust,nham/rust,aepsil0n/rust,pshc/rust,pshc/rust,ruud-v-a/rust,quornian/rust,rohitjoshi/rust,0x73/rust,zubron/rust,ktossell/rust,quornian/rust,mitsuhiko/rust,hauleth/rust,reem/rust,robertg/rust,Ryman/rust,graydon/rust,miniupnp/rust,quornian/rust,zubron/rust,erickt/rust,mihneadb/rust,robertg/rust,dinfuehr/rust,zaeleus/rust,aepsil0n/rust,aidancully/rust,jbclements/rust,philyoon/rust,seanrivera/rust,bombless/rust,ruud-v-a/rust,quornian/rust,graydon/rust,jbclements/rust,XMPPwocky/rust,miniupnp/rust,rohitjoshi/rust,victorvde/rust,hauleth/rust,achanda/rand,richo/rust,pczarn/rust,seanrivera/rust,vhbit/rust,fabricedesre/rust,TheNeikos/rust,jbclements/rust,aneeshusa/rust,aepsil0n/rust,kimroen/rust,untitaker/rust,mvdnes/rust,AerialX/rust-rt-minimal,bombless/rust,michaelballantyne/rust-gpu,omasanori/rust,mdinger/rust,jbclements/rust,0x73/rust,ebfull/rust,jashank/rust,kwantam/rust,defuz/rust,mitsuhiko/rust,philyoon/rust,avdi/rust,carols10cents/rust,emk/rust,richo/rust,servo/rust,emk/rust,zachwick/rust,seanrivera/rust,barosl/rust,kimroen/rust,victorvde/rust,zachwick/rust,pythonesque/rust,TheNeikos/rust,0x73/rust,zaeleus/rust,l0kod/rust,miniupnp/rust,quornian/rust,untitaker/rust,graydon/rust,vhbit/rust,XMPPwocky/rust,rprichard/rust,pshc/rust,zubron/rust,mitsuhiko/rust,omasanori/rust,pshc/rust,stepancheg/rust-ide-rust,defuz/rust,kwantam/rust,rohitjoshi/rust,pelmers/rust,GBGamer/rust,GBGamer/rust,mahkoh/rust,l0kod/rust,mdinger/rust,andars/rust,miniupnp/rust,gifnksm/rust,kwantam/rust,mihneadb/rust,rohitjoshi/rust,mitsuhiko/rust,miniupnp/rust,ejjeong/rust,richo/rust,jroesch/rust,pythonesque/rust,vhbit/rust,hauleth/rust,huonw/rand,P1start/rust,pczarn/rust,P1start/rust,bluss/rand,aepsil0n/rust,cllns/rust,KokaKiwi/rust,nwin/rust,pelmers/rust,l0kod/rust,dwillmer/rust,kwantam/rust,fabricedesre/rust,XMPPwocky/rust,SiegeLord/rust,barosl/rust,bombless/rust,pczarn/rust,pythonesque/rust,stepancheg/rust-ide-rust,mdinger/rust,AerialX/rust-rt-minimal,mvdnes/rust,dwillmer/rust,andars/rust,jbclements/rust,reem/rust,untitaker/rust,michaelballantyne/rust-gpu,erickt/rust,mahkoh/rust,michaelballantyne/rust-gpu,philyoon/rust,untitaker/rust,stepancheg/rust-ide-rust,ejjeong/rust,jashank/rust,michaelballantyne/rust-gpu,pshc/rust,nham/rust,mdinger/rust,ebfull/rust,richo/rust,mitsuhiko/rust,pczarn/rust,philyoon/rust,mahkoh/rust,pczarn/rust,richo/rust,P1start/rust,KokaKiwi/rust,miniupnp/rust,defuz/rust,barosl/rust,carols10cents/rust,XMPPwocky/rust,SiegeLord/rust,erickt/rust,pythonesque/rust,zachwick/rust,jroesch/rust,pczarn/rust,rohitjoshi/rust,aneeshusa/rust,carols10cents/rust,vhbit/rust,gifnksm/rust,barosl/rust,l0kod/rust,gifnksm/rust,XMPPwocky/rust,aturon/rust,graydon/rust,mahkoh/rust,cllns/rust,0x73/rust,ejjeong/rust,AerialX/rust,AerialX/rust,ejjeong/rust,aepsil0n/rust,victorvde/rust,ejjeong/rust,aneeshusa/rust,l0kod/rust,jashank/rust,bombless/rust,servo/rust,ebfull/rust,kimroen/rust,dinfuehr/rust,barosl/rust,emk/rust,fabricedesre/rust,graydon/rust,vhbit/rust,nham/rust,aidancully/rust,sae-bom/rust,XMPPwocky/rust,seanrivera/rust,P1start/rust,sae-bom/rust,fabricedesre/rust,jroesch/rust,carols10cents/rust,AerialX/rust,vhbit/rust,richo/rust,aidancully/rust,jashank/rust,rprichard/rust,robertg/rust,KokaKiwi/rust,mvdnes/rust,mihneadb/rust,ruud-v-a/rust,cllns/rust,sae-bom/rust,mahkoh/rust,aidancully/rust,TheNeikos/rust,erickt/rust,reem/rust,AerialX/rust,aidancully/rust,cllns/rust,jroesch/rust,0x73/rust,dwillmer/rust,rprichard/rust,nwin/rust,reem/rust,untitaker/rust,kwantam/rust,ktossell/rust,GBGamer/rust,aturon/rust,dinfuehr/rust