auto merge of #19961 : alexcrichton/rust/second-pass-result, r=aturon
auto merge of #19961 : alexcrichton/rust/second-pass-result, r=aturon

This commit, like the second pass of `Option`, largely just stablizes the
existing functionality after renaming a few iterators.

The specific actions taken were:

* The `Ok` and `Err` variants were marked `#[stable]` as the stability
  inheritance was since removed.
* The `as_mut` method is now stable.
* The `map` method is now stable
* The `map_err` method is now stable
* The `iter`, `iter_mut`, and `into_iter` methods now returned structures named
  after the method of iteration. The methods are also now all stable.
* The `and_then` method is now stable.
* The `or_else` method is now stable.
* The `unwrap` family of functions are now all stable: `unwrap_or`,
  `unwrap_or_else`, `unwrap`, and `unwrap_err`.

There is a possible open extension to `Result::{and, and_then}` to make the
return type further generic over `FromError` (as proposed in #19078), but this
is a backwards compatible change due to the usage of default type parameters,
which makes the two functions safe to stabilize now regardless of the outcome of
that issue.

pshc/rust,rohitjoshi/rust,andars/rust,zaeleus/rust,robertg/rust,zubron/rust,ruud-v-a/rust,AerialX/rust,jashank/rust,nwin/rust,vhbit/rust,pshc/rust,aepsil0n/rust,seanrivera/rust,kwantam/rust,kwantam/rust,nwin/rust,zubron/rust,sae-bom/rust,zachwick/rust,rprichard/rust,ebfull/rust,mihneadb/rust,philyoon/rust,ruud-v-a/rust,vhbit/rust,ktossell/rust,cllns/rust,rohitjoshi/rust,sae-bom/rust,ejjeong/rust,pelmers/rust,seanrivera/rust,XMPPwocky/rust,AerialX/rust-rt-minimal,rprichard/rust,graydon/rust,miniupnp/rust,defuz/rust,KokaKiwi/rust,aneeshusa/rust,defuz/rust,zachwick/rust,vhbit/rust,pelmers/rust,jroesch/rust,kwantam/rust,untitaker/rust,zachwick/rust,GBGamer/rust,krzysz00/rust,rohitjoshi/rust,kimroen/rust,cllns/rust,carols10cents/rust,reem/rust,zaeleus/rust,dwillmer/rust,l0kod/rust,dinfuehr/rust,untitaker/rust,cllns/rust,kimroen/rust,AerialX/rust-rt-minimal,seanrivera/rust,andars/rust,dinfuehr/rust,miniupnp/rust,philyoon/rust,zubron/rust,bombless/rust,pshc/rust,defuz/rust,vhbit/rust,zachwick/rust,bombless/rust,nwin/rust,aneeshusa/rust,ejjeong/rust,mahkoh/rust,sae-bom/rust,aidancully/rust,nwin/rust,miniupnp/rust,dwillmer/rust,avdi/rust,nwin/rust,avdi/rust,avdi/rust,bombless/rust-docs-chinese,miniupnp/rust,victorvde/rust,aneeshusa/rust,nwin/rust,krzysz00/rust,untitaker/rust,dinfuehr/rust,victorvde/rust,mahkoh/rust,gifnksm/rust,jashank/rust,GBGamer/rust,omasanori/rust,mahkoh/rust,richo/rust,AerialX/rust,untitaker/rust,mvdnes/rust,mdinger/rust,KokaKiwi/rust,reem/rust,zubron/rust,XMPPwocky/rust,pshc/rust,GBGamer/rust,graydon/rust,richo/rust,defuz/rust,mdinger/rust,pshc/rust,jroesch/rust,kwantam/rust,aidancully/rust,kimroen/rust,jashank/rust,TheNeikos/rust,gifnksm/rust,philyoon/rust,sae-bom/rust,XMPPwocky/rust,mvdnes/rust,hauleth/rust,gifnksm/rust,jashank/rust,victorvde/rust,jroesch/rust,KokaKiwi/rust,ebfull/rust,miniupnp/rust,nwin/rust,zaeleus/rust,robertg/rust,kimroen/rust,zaeleus/rust,ebfull/rust,ruud-v-a/rust,avdi/rust,zubron/rust,zaeleus/rust,cllns/rust,AerialX/rust-rt-minimal,TheNeikos/rust,KokaKiwi/rust,bombless/rust,kwantam/rust,pshc/rust,seanrivera/rust,hauleth/rust,XMPPwocky/rust,XMPPwocky/rust,GBGamer/rust,KokaKiwi/rust,cllns/rust,mahkoh/rust,kimroen/rust,jroesch/rust,ejjeong/rust,sae-bom/rust,graydon/rust,graydon/rust,gifnksm/rust,AerialX/rust,dwillmer/rust,rohitjoshi/rust,GBGamer/rust,carols10cents/rust,mahkoh/rust,pshc/rust,robertg/rust,jroesch/rust,kimroen/rust,TheNeikos/rust,cllns/rust,vhbit/rust,mvdnes/rust,jroesch/rust,reem/rust,mahkoh/rust,ruud-v-a/rust,victorvde/rust,mihneadb/rust,miniupnp/rust,richo/rust,hauleth/rust,mihneadb/rust,l0kod/rust,vhbit/rust,rprichard/rust,defuz/rust,omasanori/rust,rprichard/rust,AerialX/rust-rt-minimal,l0kod/rust,philyoon/rust,rprichard/rust,aneeshusa/rust,ruud-v-a/rust,ejjeong/rust,GBGamer/rust,jashank/rust,mdinger/rust,l0kod/rust,mihneadb/rust,reem/rust,gifnksm/rust,ejjeong/rust,pelmers/rust,GBGamer/rust,andars/rust,krzysz00/rust,jashank/rust,dinfuehr/rust,AerialX/rust,reem/rust,ejjeong/rust,zachwick/rust,avdi/rust,sae-bom/rust,zaeleus/rust,dwillmer/rust,gifnksm/rust,philyoon/rust,jashank/rust,ebfull/rust,miniupnp/rust,aepsil0n/rust,l0kod/rust,vhbit/rust,aepsil0n/rust,l0kod/rust,omasanori/rust,avdi/rust,reem/rust,robertg/rust,dwillmer/rust,graydon/rust,hauleth/rust,carols10cents/rust,untitaker/rust,richo/rust,robertg/rust,andars/rust,jashank/rust,mihneadb/rust,jroesch/rust,bombless/rust,mihneadb/rust,dwillmer/rust,andars/rust,TheNeikos/rust,philyoon/rust,graydon/rust,dinfuehr/rust,l0kod/rust,zachwick/rust,kimroen/rust,ktossell/rust,ebfull/rust,hauleth/rust,mvdnes/rust,XMPPwocky/rust,carols10cents/rust,TheNeikos/rust,aepsil0n/rust,ktossell/rust,AerialX/rust,carols10cents/rust,omasanori/rust,AerialX/rust-rt-minimal,seanrivera/rust,pelmers/rust,aepsil0n/rust,andars/rust,aidancully/rust,dwillmer/rust,rohitjoshi/rust,richo/rust,jroesch/rust,carols10cents/rust,KokaKiwi/rust,robertg/rust,seanrivera/rust,krzysz00/rust,mvdnes/rust,aidancully/rust,l0kod/rust,aidancully/rust,mdinger/rust,defuz/rust,untitaker/rust,dwillmer/rust,zubron/rust,dinfuehr/rust,kwantam/rust,pshc/rust,AerialX/rust,nwin/rust,aneeshusa/rust,rprichard/rust,zubron/rust,mdinger/rust,aidancully/rust,krzysz00/rust,ruud-v-a/rust,victorvde/rust,aepsil0n/rust,ktossell/rust,aneeshusa/rust,pelmers/rust,TheNeikos/rust,bombless/rust,miniupnp/rust,zubron/rust,vhbit/rust,rohitjoshi/rust,ebfull/rust,ktossell/rust,victorvde/rust,AerialX/rust-rt-minimal,krzysz00/rust,ktossell/rust,omasanori/rust,omasanori/rust,pelmers/rust,ktossell/rust,GBGamer/rust,hauleth/rust,mvdnes/rust,bombless/rust,mdinger/rust,richo/rust