Prefer .ruby-version to .rbenv-version for reading local versions
Accept "ruby-" version prefix but print a warning to stderr
Read both .ruby-version and .rbenv-version, but write (and migrate to) .ruby-version
Tweak the ruby- prefix warning
Document .ruby-version
Clarify that .rbenv-version is removed when migrating
Merge pull request #302 from sstephenson/ruby-version

Support for .ruby-version files
"per-project" -> "application-specific"
"binary" -> "executable"
Tone down the RVM incompatibility notice
Update the uninstallation section
"Usage" -> "Command Reference"
Prioritize `rbenv local` over `rbenv global` and `rbenv shell`