Update unit tests

[Eric Harper]

Need more unit tests, need them to be updated

[Richmond Newman]

Harper in the branch I made called fixed_unit_tests, can you fix the failing PMFT2D related tests? Probably is just a minute of copy paste.

Also: I presume you wrote the examples (RDF, PMFT, PMFTXYZ?). These all look for a mystery 'start.xml' that isn't included. One probably should be included, or they should switch to at least run off of randomly generated ideal gas configurations.

[Eric Harper]

Not sure to what you are referring. 'start.xml' is no where to be found. The issue is just the api change.

[Eric Harper]

All unit tests pass

[Richmond Newman]

Oh, the examples don't work, for reasons of both the API change, and that they try to load an XML file that does not exist. At some poitn freud might want to ship w/ at least a few functional examples. At least the RDF example should work. If not reading from an XML, at least generating an ideal gas and then computing the RDF on it.

Technically, is separate issue from the unittests, but fairly similar. The only working "Examples" are now the unit tests. Which isn't that terrible I guess.

[Eric Harper]

Examples can be updated, unit tests are more important. In fact, you should create an issue re: examples