Compile for Mono

Fix warnings that appear on Mono, and use a shell script to perform post-build step so it works with both Visual Studio and MonoDevelop.

I've been using your library on Mono and, in order to make it perform the post-build step I use a trick which may be too hacky for you to want to accept this pull request. Since I know the user has git installed (in order to check out this github repo), I write the PostBuildEvent step as a bash script, which works on Mac and Linux (because they have bash) and Windows (because git-bash is installed). I also fixed a number of compiler warnings, mostly by disabling them in the .csproj file.