Updated contributor branch references - 2.0 no longer maintained

The current documentation refers throughout to making bugfix and
corrections against the 2.0 branch, however this is no longer
maintained. Updated with references to 2.1 to make this more
obvious to new contributors.
Update generic_event.rst
Merge pull request #2503 from acoulton/updating-contrib-branch-refs

Updated contributor branch references - 2.0 no longer maintained
[#2504] Adding some better headers to the Process component
Merge branch '2.1' into 2.2

Conflicts:
	components/process.rst
[#2504] Backporting information about stopping a process
Merge branch '2.1' into 2.2