Giant Merge

In Which Dan Dumps the Last Four Years of His Life into Trackpy

All tests pass. I made some changes to glue it all together. Notably:

* soft-matter/pims is a dependency.
* As planned, ``identification.py`` is gone, replaced by the more complete and tested ``feature.py``, which I am open to renaming.
* setup.py is more complex, derived from what pandas does. The version number automatically generated based on the tagged git release, and untagged commits get a version number like 0.1.0-352-r23ff2, i.e., with a counter and a commit hash tacked on.

I'd like to merge this soon so that I can use my tests from mr while I'm attempting to merge Nathan's code. But I'll wait for Tom's blessing on the [README](https://github.com/danielballan/trackpy/tree/merge-mr). (Do you want to tack your grant(s) on there also?) Of course I can hold off if anyone spots a major problem.