add chunk_ranges function to iterutils

[jstriebel]

This PR adds a chunk_ranges function to iterutils, which doesn't chunk an iterable or list directly, but produces the relevant indices to chunk it. It contains functionality for windowing/overlap (see also issue #310) and alignment of the chunks. I'm not sure if input_size or input_end is more appropriate for the arguments, also the function name might need improvement.

It would be great to incorporate this function into boltons IMO, thanks a lot for considering this.

This PR includes the function itself, a test, and updates the docs.

[jstriebel]

@mahmoud Friendly ping :-) What do you think about adding those changes?

[mahmoud]

Hey thanks for your patience (#newdadlife over here), and thanks for the PR!

From what I see:

• It's performing non-trivial work
• It's tested
• It's documented
• It follows the boltons architecture

So let's go for it :)

[jstriebel]

Thank you for maintaining this lib, @mahmoud!