trackpy: Trackpy v0.4

This is a major release that includes new choices for linking and feature-finding algorithms, as well as many performance increases and clean-ups. It is recommended for all trackpy users, but may require minor changes to existing code, as detailed below.

See http://soft-matter.github.io/trackpy/v0.4/whatsnew.html for a full overview of the changes.

Note: Full list of contributors: Aron Ahmadia, Thierry Bottaro, François Boulogne, Zoey S. Davidson, Rebecca Perry, Al Piszcz, Chaz Reid, Jan Schulz, Leonardo Uieda, and Devin Wieker