fix mono 3 rewrite and test-specific issues

use normal threads instead of Task Factory to test less multi-threading (Task Factory seemed to act up on mono 3)

Update Platform.cs

Update Platform.cs

use first version found

refine mono version comparison (URI issue doesn't seem to be fixed in all Mono 3 versions)

change nunit to nuget reference, include runners

fix hogan / coffeescript failure test threshold

rewrite CSS paths without using URI class
- this has all unit tests passing in mono 3.0.7 and 2.10.8.1 at codebetter
  (#241)

fix #241
Merge commit '5b899cd'