WinHelp, SHG, MRB: add tests

[ForNeVeR]

Currently, Oddities.WinHelp completely lacks any tests. We should add them.

It's quite hard to find any test data for the library, though. I'm not aware of any modern tooling that would allow creating a .hlp file, and also I'm not aware of any free .hlp file samples (that we could commit into the repository to use as test data).

We'll have to find some.