refactor: replace file system constants with IFileSystem
build: reverting mis-committed CommonVersionInfo.cs (from July 2013)
add Linux build instructions to readme
Merge pull request #738 from adamralph/replace-filesystem-constants

replace file system constants with IFileSystem
Updated PackagesFile, PackagesFolder, BinFolder, DllCacheFolder, NuGetFile to be virtual
Merge pull request #744 from pvcbuild/dev

New FileSystem properties should be virtual
refactor: remove console noise from Mono engine when platform is Mono