pytagtime: plot title shows date range
pytagtime: correct nan handling for top-n tags
pytagtime: improve pie-chart absolute values if some weekdays are omitted
pytagtime: add license
pytagtime: cumulative trend plots as in beeminder, hour-limits, tag maps, save to file
pytagtime: more cleanup, nicer trend plots
Merge pull request #33 from temporaer/master

pytagtime: beeminder-like cumulative trend plots, show work hours only, save to file, bug fixes  and cleanup