Preliminary support for emscripten under Visual Studio.
Emscripten support for the vs2010 generator and proper support for per target file listing.

The file key now correctly collects files across all configurations and not just at the project level.
Also fix an error regarding the skip_files key in the core documentation.
Few syntax improvements.
Properly implement binary extensions in all add-ins of the vs2010 generator.
Fix binary extension for all generators and addons, add html output to the Emscripten addon.