BLD: Add a conda recipe that builds binary package from current git rev.

This is the "conda recipe" I have been using to create the conda packages in trackpy's development channel. By including them in the repo itself, it will be possible to make Travis build conda packages and upload them to binstar. ([Others](https://github.com/rmcgibbo/python-appveyor-conda-example#binstar) have already figured out the details of how to do this.)

FYI, the dev conda packages are up to date. Anyone who wants to take the improved 3D capabilities for a spin can easily [install the latest development version](http://soft-matter.github.io/trackpy/installation.html#latest-version-under-development). attn: @mmdriscoll
I have had good success with 
```
 version: {{ environ['GIT_DESCRIBE_TAG'] }}.post{{ environ['GIT_DESCRIBE_NUMBER'] }}
```

which will give versions like `0.2.3.post53`