Include caveat about OS X llvm/clang incompatible rubies
Merge pull request #104 from trek/document-osx-specific-issues

Include caveat about OS X llvm/clang incompatible rubies
Spacing.
Wording.
Added Caveats for Rubinius and JRuby.
Wording.
Markdown
Renamed Caveats to Known Issues.
Update Ruby 2.1 to ruby-2.1.0-rc1.
Add MD5 for ruby-2.1.0-rc1.
Bump suggested brew gcc from 4.7 to 4.8.

Mavericks require gcc between 4.4 and 4.8.
Add mention of brew --HEAD for install from trunk.
Capitalize brew --HEAD sentence for consistency.
Add rubinius-2.2.2 MD5.
Set rubinius 2.2 and stable to 2.2.2.
Add ruby-2.1.0 as stable.
Add ruby-2.1.0 MD5.
Update Readme.md

Fix brew url
Merge pull request #107 from georgebellos/master

Fix brew link.
Also bump 'ruby 2' to 2.1.0.