allow switch abbrevations as an option

[presto8]

One feature I missed from argparse is the ability to have abbreviations or partial switches (such as "--foo" matching "--foobar", assuming no ambiguous conflicts). This patch attempts to add that. I also added a unit test and it seems to pass. I'm not sure if the authors are in favor of this feature, but sharing it in case it would be beneficial to others.

P.S. I looked around in the code and docs for an already existing implementation, I hope I didn't miss it and do redundant work :-)

[coveralls]

Coverage increased (+0.05%) to 82.254% when pulling ee4eba9 on presto8:master into 2b5a82a on tomerfiliba:master.

[henryiii]

Nice, as long as it's optional (it is) I like it. Would you like to add a note to the docs?

[presto8]

Thanks! Sure, let me update the docs, rebase the change and update the pull request.

[henryiii]

Ignore the drop in coverage, it is because the Travis 2.6 build originally failed and I had to rerun it.

By the way, when you say for "backward consistency", it's also there to reduce the possibility of a typo. I think this was actually listed as the main reason Plumbum does not simply sit on top of argparse in the current documentation. Argparse even gained the ability to not match partial arguments in Python 3.5 with allow_abbrev.

I wonder if a similar addition could be make to CLI11...

[henryiii]

One final note: this could be very useful as a helper for adding tab completion support someday also...

[presto8]

I added some docs, I tried to match the style of the existing docs. And that is a good point about typos!

[henryiii]

Looks good to me, thanks!

[presto8]

Thank you, as well, for all of your hard work on this great project!