#19 Add support for .NET 4.5

[Oren Hurvitz]

This patch adds support for .NET 4.5 and .NET 4.5.1.

There are two minor additional things that should be done and aren't included in this patch:

1. Update Prebuild.exe. I assumed you'll want to compile it yourself.
2. Add to the svn:ignore property of the "Prebuild" directory the following entry: "Prebuild.v12.suo". This is the SUO file creatd by Visual Studio 2013. I didn't add it because that made "svn patch" fail, for some reason.