Fixes #296 - Assembly reference missing with ..

* Wrote unit test to prove failing path resolution
* Implemented change suggested by @khellang (Use `GetFullPath`)
Refs #296 - Ensure that the method returns a directory path

Ensure that the method returns a directory path and not a file path.

Requires that the path have a trailing slash to indicate that it is a
directory. Not really sure how to avoid this?
Using correct assertion library and returning the correct path if the path is a filename or directory. Would prefer if it was all in memory, but unsure as to how it should be designed.
Merge pull request #304 from SpikeTheMaster/dev

Fixes #296 - Assembly resolution