CLN: Tabs -> spaces
ENH: Cach velocity vectors to avoid reading JSON data after the first time through
DOC: Comment string for points
ENH: Keep a constant scaling factor at different zoom levels
CLN: spaces-> tabs again
Merge pull request #10 from enthought/enh/cache-velocities

Cache velocity data
Ensure drawing updates are asynchronous
Merge pull request #13 from enthought/enh/async-vector-update

Ensure drawing updates are asynchronous
Merge remote-tracking branch 'origin/master' into enh/scale-with-zoom
Merge pull request #14 from enthought/enh/scale-with-zoom

Enh/scale with zoom
Merge remote-tracking branch 'origin/master' into gh-pages