Django-heroku-connect

- use recapture when doing `redo` on ordered-write errors 98

changes:
- revert the index on `is_deleted` fields (https://github.com/Thermondo/django-heroku-connect/pull/97)
- make wrong db-contraints on FK an error, not a warning (https://github.com/Thermondo/django-heroku-connect/pull/94)

Added

- `MANIFEST.in` for a better package

Changed

- Drop Travis matrix to unblock Travis stages (this was also preventing the PyPI release process)

Changed

- CI: Added a separate stage for publishing package in PyPI (https://github.com/Thermondo/django-heroku-connect/commit/8d07c3fabb4a6e3f0d02036e7e36aa0e98f69d41)

Changed

Fix Travis config to trigger PyPI releases (0.19.0 was not released due to that).

Added
- `is_deleted` now contains `db_index` (https://github.com/Thermondo/django-heroku-connect/pull/85)

Changed
- use absolute imports all over the code (https://github.com/Thermondo/django-heroku-connect/pull/87)
- use `tox-travis` for better and simpler CI configuration (https://github.com/Thermondo/django-heroku-connect/pull/88)
- documentation fixes (https://github.com/Thermondo/django-heroku-connect/pull/78 and https://github.com/Thermondo/django-heroku-connect/pull/79)