Update RELEASES.txt

Fix Typos
Fix #15453
Improved example in the Guide

Fixes https://github.com/rust-lang/rust/issues/15452
auto merge of #15447 : patrickyevsukov/rust/patch-1, r=alexcrichton

Fix Typos
auto merge of #15454 : jakub-/rust/15453, r=huonw

I forget we now have byte string literals.
auto merge of #15456 : aochagavia/rust/guide, r=alexcrichton

Fixes https://github.com/rust-lang/rust/issues/15452
Merge branch 'master' of github.com:rust-lang/rust into lets-get-it-compiling
All tests now pass.