Add support for ImageURL scaling
Allow to anchor ImageURL to corners and center
Add glyphs/image_url.py example
Use "top_left" if @mget("glyphspec").anchor gives nothing
Update ImageURL's tests
Expose DatetimeTickFormatter.formats in Python API
Show how to use DatetimeTickFormatter in daylight.py example
Add DatetimeUnits enumeration for DatetimeTickFormatter.formats
Merge branch 'master' into datetime-formats
Sort DatetimeTickFormatter's formats by their "size"
fix #567
add new exercise to tutorial and also sub-project for building just tutorial (still needs some fixups)
Merge pull request #569 from mattpap/image-url-scaling

Scale and anchor ImageURL and add an example
Merge pull request #577 from mattpap/datetime-formats

Expose DatetimeTickFormatter.formats in Python API and add an example
Merge remote-tracking branch 'origin/master' into widgets1
Make Select more flexible with respect to options
Catch KeyboardInterrupt in app/downloads example
Add glyphs/population_server.py example
Add serialization of relativedelta
Format months in app/downloads example