0.5.3

Changes:

• Added 'RESET_PASSWORD_FAIL_WHEN_USER_NOT_FOUND' setting key (issue #81)
• Added login fields unique system check (issue #91)
• Limited Django to <3.0 (due to some incompatibility issues - limit will
  be lifted in 0.6.*)
• Added Makefile (issue #88)
• Added French message translation (pull request #85)
• Added Contributing Guidelines (issue #64)
• Various test code refactors