Improvements:
- Added support for negative timestamp (#1060)
- Fixed PytzUsageWarning for Python versions >= 3.6 (#1062)
- Added support for dates with dots and spaces (#1028)
- Improved support for Ukrainian, Croatian and Russian (#1072, #1074, #1079, #1082, #1073, #1083)
- Added support for parsing Unix timestamps consistently regardless of timezones (#954)
- Improved tests (#1086)