New feature: 'iter_matches'

[neysofu]

Relates to #1206.

I've added support for iterating over ArgMatches in an ordered manner. This feature ships with a new opt-in dependency, indexmap.

It is still a WIP, more specifically I need to:

• add a new method to ArgMatches to hide implementation details over ArgMatches.args;
• write its docs; and
• add some tests (forgive me, for I have sinned).

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This change is 

[mention-bot]

@neysofu, thanks for your PR! By analyzing the history of the files in this pull request, we identified @kbknapp to be a potential reviewer.

[kbknapp]

Looks like a great start! 👍

You could probably also use src/map.rs as a guide since it's doing something very similar with VecMap instead of IndexMap.

[XX]

@neysofu @kbknapp Are the changes still pending? Is there something I can do to help?

[neysofu]

@XX I've had some other things to do, but I promise I'll get back to it. I would say ETA is 1 week or less.

[XX]

How about completing this PR?

[Dylan-DPC-zz]

Thanks for the PR. I'm closing this since it was inactive and clap is on track for a new major release. If you are interested in this, or anyone else wants to pick it up, you can send a PR