Add correct optional default start/end parameters to str count, find,…

[gwk]

… index, rfind, rindex.

This supersedes PR #1107, and fixes #1108.

I reviewed the corresponding annotations for byte and bytearray; they look correct but use the x: int = None style which @JelleZijlstra says is discouraged. Perhaps those should be cleaned up separately?

[JelleZijlstra]

Thanks, this looks fine to me but I'll wait for @gvanrossum before merging.

[gwk]

Also filed #1110 for the remaining __index__ concern, which I cannot take on at this point in time.

[gvanrossum]

OK, but...

• This also needs to happen for Python 2
• These functions only take keyword args -- by convention we'd use __start etc.

[gwk]

@gvanrossum just pushed an updated commit addressing your concerns.

[gvanrossum]

Thanks for the quick response!