Minor features and bug fixes:-
- update dependencies for security patches
- add an option for flat folder structure YYYY-MM (thanks @idoroseman)
- add an option to rename the photos and albums folders (thanks @idoroseman)
- fix date range bug on --rescan
- fix extraction of EXIF description into DB on comparison
- fixes to make the comparison feature more accurate with duplicate file names
- add --favourites-only flag
- add Python3.6 to the Travis test matrix
- add readme for Python3.6