trackpy: Trackpy v0.3.0

This release is strongly recommended for all users, as it brings major improvements in speed and 3D feature-finding, and many other functionality and accuracy improvements. Please be sure to read the "What's New" page in the documentation before upgrading, especially the item under "Enhancements" about calculating masses. You may have to make minor edits to your scripts and notebooks to use them with v0.3. If you are an Anaconda user, upgrading is as simple as "conda update -c soft-matter trackpy". Other methods are shown on the Installation page in the documentation.Full list of contributors: Aron Ahmadia, Continuum Analytics; François Boulogne, Princeton University; Rebecca Perry, Harvard University; Al Piszcz, The Mitre Corporation Jan Schulz, TU Freiberg; Leonardo Uieda, Universidade do Estado do Rio de Janeir