Django-pg-bulk-update

Bug fixes
1. issue-63 fix by ryanhennig: already quoted table names formed wrong SQL
2. Partially fixed `auto_now` tests bug with local timezone differring from UTC

Documentation
1. Added manual for running unit tests locally (by ryanhennig)

Features
1. Added ability to create set functions which doesn't require value (`SetFunction.needs_value` attribute)
2. Added `NowSetFunction`

Bug fixes
1. Fixed [issue 55](55): `auto_now` and `auto_now_add` parameters of `DateTimeField` and `DateField` now work correctly
2. Fixed tricky issue with checking default connection during library import, which caused wrong default connection settings
3. Fixed django 3.1 compatiblity
4. Fixed django 4.0 JSONField deprecation warning

Testing
1. Replaced django 1.7 with 3.1 in travis tests

Performance
1. Optimized SQL in VALUES section, so that defaults are not copied a lot of times in bulk_create and bulk_update_or_create
2. Other performance imporvements

Bug fixes
1. Fixed SQL bug in bulk_update_or_create query when update=False and returning is used

Features
1. Added bulk_create helper to queries
2. Added pg_bulk_create function to QuerySet

Minor imporvements
1. Prevented adding NULL values as defaults when django field has no default value

Bug fixes
Fixed issue https://github.com/M1hacka/django-pg-bulk-update/issues/51