Merge pull request #428 from pulp/mhrivnak-231-release-notes

adding 2.3.1 release notes
Update doc versions to 2.4.0.
Change the doc versions to 2.3.
If the API call specifies a checksum of null/None use the default
1053674 - implement distributor_removed on yum distributor
1046160 - giving up ownership of /var/lib/pulp/published
Update for PR comments
Merge pull request #443 from pulp/barnabycourt-1053674

1053674 - implement distributor_removed on yum distributor
1064594 - initializing plugin loader for migration 0015
fixing a typo in a filename
Merge pull request #446 from pulp/mhrivnak-1064594

1064594 - initializing plugin loader for migration 0015
Merge branch 'master' into mhrivnak-1046160
moving ownership of /var/lib/pulp/published to the platform's pulp-dev script
Merge pull request #444 from pulp/mhrivnak-1046160

1046160 - giving up ownership of /var/lib/pulp/published
Fix the repo publish and stop eating the exception if something fails
Merge branch 'master' into distributed-tasks
Merge branch 'rbarlow-doc_versions'
Merge branch 'pulp-2.3'

Conflicts:
	docs/tech-reference/conf.py
	docs/user-guide/conf.py
Merge branch 'master' into distributed-tasks
Merge branch 'distributed-tasks' into barnabycourt-fix_cli_publish