Implemented ShouldRenderFile

Please review.
Correct :)

While we are at it let's delete that method we marked `[Obsolete]` at the same time, also while we are at it can you put the release notes to mention the breaking changes file like I did in Seleno:

* https://github.com/TestStack/TestStack.Seleno/blob/master/TestStack.Seleno.nuspec

Also, we should have a think if there are any other breaking changes we want to make so they can all be made at once.

Also, having a `readme.txt` file in the root package will pop it open - we can include mention of the breaking changes file and other files like I've done in ChameleonForms:

* https://github.com/MRCollective/ChameleonForms/blob/master/ChameleonForms/readme.txt (note the readme.txt is in the subfolder of the project so it doesn't trample on the main readme.md file)
* https://github.com/MRCollective/ChameleonForms/blob/master/ChameleonForms.nuspec (note how readme.txt is included in the nuspec - we have the two nuspecs for this project - make the .mvc3 one reference a readme.txt in ../FluentMVCTesting so we don't have to duplicate the content).

Let me know if this doesn't make sense and I'll try and explain better :)