Easy indentation for menu options

[pineapplethief]

I'm hacking on highline for rails template generator of mine and want menu options to be nicely indented when printed, but I've found no easy way to do this.
I think that adding :index_prefix accessor and/or :indent_options accessor to Menu class could be useful for customizing menus. I also spotted hardcoded dependency in highline.rb choose method, which makes using custom menus subclassed from Highline::Menu quite challenging. I can't think of easy way to inject dependency there though because of *items in args list.

[abinoam]

We're working on 2.0.0 and the main focus is refactoring and trying to
decouple things to be more reusable. You can see this by taking a look at
the last PRs and the diff between master and 1-7-stable branches.

I may try to have a quick look on your issue this week. But if you want,
feel free to go on trying a little more and feel free to ask any question.
I and @JEG2 can give you any assistance you need. And now we have @matugm
that are getting used to the code base also.

[pineapplethief]

I would love to help but how could I contribute? Section on contributing in readme would be helpful I think.

[abinoam]

Feel free to:

1. Fork the repo
2. Commit
3. Push
4. Make a Pull Request
5. We're gonna give you suggestions and if everything fits well we're gonna merge it.

But, don't be pressured to do that!