Enable `thisweek` option, add month options for due dates#259

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ltrubov wants to merge 2 commits intogammons:mainfrom ltrubov:fix-thisweek

+42-7

Commits on Oct 14, 2021

thisweek accepted, thismonth, lastmonth, nextmonth added; treated as single days for listing (monday or first of month)
ltrubov
committed

Commits on Oct 15, 2021

proper filtering from due:thisweek, due:nextmonth, etc
ltrubov
committed