Add NuGet support

This pull request adds a NuGet manifest (.nuspec file) to the repository. It allows you to easily create a NuGet package and ship the project through NuGet.

You can do this automatically upon commit using [MyGet.org](http://www.myget.org) build services (free for OSS! contact us at info@myget.org). If you want I can set this up for you, just reply to this pull request for further details.

Main idea: continuously package the UniformJS sources in a NuGet package and have it on MyGet.org on your own feed so people can test it. With a click of a button you can then push the package from MyGet to NuGet (upstream package source) and release it to the masses. This very simple workflow is also [explained on our blog](http://blog.myget.org/post/2013/03/06/MyGet-Build-Services-Package-Versioning-Explained.aspx).

FYI: I currently already have a package [jQuery.Uniform on NuGet](http://nuget.org/packages/jQuery.Uniform/1.7.5.2), I'd happily transfer ownership to you.