VB -> C#: Improve query syntax support

[GrahamTheCoder]

#29

Problem

Currently don't handle several keywords, or nested statements

Solution

• First step was to handle nested statements by chunking sections together.

• At least one test covering the code changed

• All tests pass

Which part of this PR is most in need of attention/improvement:

• The higher level methods in the QueryConverter are pretty much write-only code. They just batch up bits of the query for other methods to handle later, but are missing appropriate naming and probably a data structure of their own.
• The lower level methods still don't handle many cases, currently they will just throw an exception due to using Single in places where there can be multiple elements - I don't have examples of the more advanced cases, so I think this is fine for now, and better than barreling on missing information without informing the user.

[GrahamTheCoder]

I think I'd like to write a few more tests to get this bit merged before moving on to the other points. I'm slightly worried some cases may be worse on this branch still