Bump version to 0.10
Minor adjustments to the 0.10 release notes.

Mention another lint, fix a typo, and rearrange some things.
Update AUTHORS.txt for 0.10
Tweak the installation instructions in the README

Update the instructions to reflect that we have binary installers for all
supported platforms, and move the building from source directions into a
dedicated "Building from Source" directory.
auto merge of #13286 : alexcrichton/rust/release, r=brson

Merging the 0.10 release into the master branch.