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.