Added Visual Studio 2013, Windows SDK 8.1 and native/cross amd64 compiler support
Added Visual Studio x86 and ARM cross-compilers
Improved Visual Studio version and supported architecture tracking
Added target platform handling to the library, include and resource compiler selection
Improved cross-compiler detection mechanism
Added Windows SDK 8.0 default path
Prevent warning about extracting GCC version on OSX 10.9

- Detect Xcode version of gcc and don't treat as GCC tool chain
Merged pull request #219 from mputters/vs2k13-winsdk8.1
Minor tweaks to VisualStudioLocator and VisualStudioInstall
Mention Visual Studio 2013 contribution in release notes
Fix partial commit: details of Visual Studio location improvements in release notes