add create-releases feature

[vdice]

Add deisrel create-releases <params> <opts> command/functionality, enabling the following workflow:

deisrel create-releases <params> <opts> -> creates releases for all repos using the appropriate GH api call, specifying same tag & title for each release and repo-specific changelog for its POST body (can use existing deisrel changelog functionality to derive) -> command returns by printing collated/aggregated changelog to stdout -> user copies & pastes, sends to Marketing, etc. for blog announcement(s).

Where <params> includes release_tag and release_title (possibly same string)

Where <opts> includes, minimally, a --ref <ref> flag for passing in a different ref other than master to create release from. (Should also consider a --dry-run flag, or, alternatively, a prompt to proceed after supplying info on what will be done.)

[vdice]

This ticket is no longer valid/relevant now that we are releasing components individually.