Add hourly support to timeseries

This helps support #32 and #42. We could support other intervals, as
well, with a simple addition to the processData method. However, right
now we only support "hourly" and "daily", and intentionally barf on
other intervals.

Note that hourly data gets big (30k+ points) for some data streams, so
it might make sense to implicitly or explicitly limit the amount of data
transferred (say, only in the last year, so ~9000k points). Or maybe a
point count. Anyways, something needs to be done because the data
volumes get unmanageable.
Use circular average for wind direction

This was a bug in glac.io until now. Thanks to @mdsmith for help nailing
this one to the wall.
Fix bug in circular rendering
Add wind rose visualization for Hubbard Glacier

This commit includes the basic ground work for wind rose visualization.
At this point we're definitely in demo mode. We need to add
visualizations for other glaciers, do some month-by-month work, and
more. But it's a start.

This commit should be rebased before merging.