Ease E858/E860 errors debugging

E858: Eval did not return a valid python object
E860: Eval did not return a valid python 3 object
Purge cache on BufWrite

Instead of much simpler solution define an API that may be used for anybody
willing to add cache purging on events with a few keystrokes
Make spaces around the divider configurable

Fixes #225
Fix icon_names for unknown weather code