Make API documentation available online

[medovina]

As far as I can tell, the API documentation for SFML.NET is not available online.

It looks like the build process for SFML.Net will build the API documentation using the Sandcastle project file doc/sfml.shfbproj in the SFML.Net source distribution. However, I think that will only work on Windows. I'm running Linux, so I believe I have no way to generate the API documentation myself.

I might try to install Windows in a virtual machine to run the build process, but that's a bother. It would be much more convenient if the API documentation was simply available at some URL.

[eXpl0it3r]

See also #275