Not all of diff types documented and used in iter_change_type

[worldmind]

Here, in comments five types described (not sure that this comment needed because same info in docstring), but below six types in change_type, in docstring here 5 types and here 5 types processed. Looks like type 'C' not described, but processed and 'T' described but not processed.

[Byron]

Absolutely right, thanks a lot for taking the time to point this out. It would be great to see a PR to improve this, such that

• the comment is deleted
• the doc-string is updated to include the ‘C’ change type
• the processing for the ‘T’ change type is added

[worldmind]

I will be glad to prepare a PR, but I am even can't understand what is going on in code because on first look it can be replace by such code:

for diff in self:
    yield diff

but may be I miss something and some diffs must be excluded from iteration?