Ci, mono and documentation

This pull requests adds CI, mono support and more documentation (see http://matthid.github.io/RazorEngine/) to RazorEngine.

### More changes:
* The project structure was updated to integrate CI and make building from command line more straightforward (just "./build" or "./build All").
* You can build everything via "./build Release" (complete project + docs + release + nuget) or single things like "./build NuGet_single" (only nuget package).
* Documentation is build from source and the /docs folder. I collected some docs hanging around on various pages and wrote some pages myself.
* Re-Added net40 support (will use older dependencies automatically).
* Fixed some bugs (see commits for details)

### Left for the merger or this pull request (as I'm unable to do it):
* create AppVeyor and Travis accounts and link them to the repro.
* update links to the new documentation (from http://matthid.github.io/RazorEngine/. Just edit https://github.com/matthid/RazorEngine/blob/develop/buildConfig.fsx#L48.
* Change the version back (edit https://github.com/matthid/RazorEngine/blob/develop/buildConfig.fsx#L34)!
* Edit https://github.com/matthid/RazorEngine/blob/develop/nuget/RazorEngine.nuspec (metadata/id, licenseUrl, projectUrl)
* Run "./build Release" (and answer "y"), this will
   * Update the version, build and test the project
   * Create and push the initial docs to your fork ("./build Release")!
   * (optional) Release a new nuget package ("./build Release" already created the package in release/nuget)
* (optional) You should switch to "git flow" (ie work only on the develop branch and release to the master branch) or just remove the "develop" build badges from the readme.

### Notes:
* Possibly now you need to "./build" before the .sln file work (This is properly documentated in https://matthid.github.io/RazorEngine/DevelopReadme.html)
* You can always get back to me if anything doesn't work as expected.
* It's possible that I missed something...