Use params keyword

Howdy,

I recently found your project and it was exactly what I was looking for!  I needed to convert some MbUnit style tests to MsTest.  Adding the required methods was easy and works great.

I thought I would try to contribute to the project.  So, as a first pass, I put together this update that makes use of the params keyword to reduce the number of methods in MsTestExtensions.cs.  I added MsTestExtensionsTest.cs to demonstrate this approach works.

Thanks,
jdb