Faster Runtime Compiles and Improved Compiler support

Recent code changes have concentrated on getting faster runtime compiles, and improving compiler support.

• The Posix compiler (for Linux and OS X) now outputs intermediates. Motivated by a request from Github user procedural, I finally got around to getting this to work. I've seen up to a 2x performance boost on repeat compiles, and small compile times are now much shorter than a second. Developers should be aware that they may need to clean their runtime Intermediate folder via the IRuntimeObjectSystem::CleanObjectFiles() function.
• Visual Studio 2015 is now fully supported from both upgrading the solution or generating with cmake. After reading Bruce Dawson's excellent post on /DEBUG:FASTLINK I've added support for this to compiles, with generated pdb's being much smaller and runtime compiles faster. Thanks to github user Ashalah for spotting I had the VS2015 version number incorrect as MS skipped 13!
• CMake support for OS X has been added, so developers can use this instead of the included XCode project if needed.
• Runtime dependencies have been extended to support arbitrary file and extensions. See the documentation on the wiki for more details.
• Added cmake install support from Github user kubaroth.