Add unit tests for .NET code

[gregmac]

Existing code has some tests only for the parser, and there's no test for any of the actual API (for example, I would have made a test to illustrate #3 but there's no test framework).

Now that #2 has been merged, are you open to adding some unit tests? Obviously Travis will have to run them, but any preference on test framework (NUnit vs others)?

[laktak]

That's great! 👍 I haven't used NUnit so I'll leave that up to you (as long as it works with travis/mono and is "easy" to set up).

[laktak]

Closing for now.