Finish tranisition for new revisions syntax.
This change does a handful of things:

* Updates the ClearCase implementation to use the new diff method, and changes

  it from using --tracking-branch to a brtype: prefix.

* Fixes up ClearCase documentation for the new syntax.

* Cleans up the get_diff method, now that there are no legacy consumers.

* Changes the --revision-range argument to just print an error.

* Changes the help for the options to say [revisions] instead of

[changenum].

* Updates the docs to remove --revision-range

* Updates the docs to list -I/--include

Ran unit tests.
Built docs and verified that they looked right.