Added support for new option LISTINGS_FOLDERS.
Fixed ReST listing directive.
Removed flake8 warnings.
Added suggestions by Kwpolska.
Forgot to check in part of code.
Always adding .html. Should fix problem when including .html files, for example via the ReST listing directive.
Fixed syntax error and added more comments.
Moved entries to top.
Added another missing piece.
Added documentation.
Fixed missing parameters.
Improved code.
Links should now be correct.
Extended FakeSite's config so that tests with ReST compiler won't fail (due to change to its listing plugin).
Making flake8 happy.
Improved config fallback.
Undid invalid change.
Simplified (and corrected) duplicate output folder check.
Input folder check is unnecessary since LISTINGS_FOLDERS is a dict(), whence keys are unique.
filter out all untranslated posts (via #1360)

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
better handling of dates

Signed-off-by: Chris Warrick <kwpolska@gmail.com>