Set leaflet map view by URL fragment

This could be improved somewhat, but it's functional. It will still need
a button to set the view fragment.

Ref #145
Improve URL fragment processing
Merge branch 'master' into f.view-permalink
Add permalink auto-updating

When the map is dragged, the URL fragment should automatically update
with the current zoom level and coordinates.

Close #145
Version 0.5.11