chore(package.json): add commit message format helper script

[kwonoj]

This PR adds one additional script command npm run commit, which invokes cli based step by step commit message formatter follows convention in contributing guideline to help anyone who are new to codebase can easily compose commit message.

See how does wizard works in action:

What's required if I don't need this helper but I can control git by myself completely?
: Do not need anything. Unless explicitly invoke npm run commit command, helper won't be able to do anything. This applies GUI client also, currently there isn't way hook this helper with GUI client.

[staltz]

Love it

[luisgabriel]

👍

[benlesh]

This is very cool. @IgorMinar @jeffbcross you might benefit from this module on the angular project if you're not already using it.

[kwonoj]

Honestly, I am inspired by angular repo's open issue (angular/angular.js#12730) and adopted into here first 😉

[benlesh]

merged with 5f68356... great stuff, @kwonoj

[jimthedev]

@kwonoj per your comment about Git GUIs I've opened commitizen/cz-cli#45 to track this idea. Thanks!

[kwonoj]

@jimthedev It is so appreciate! I was actually curious if it could be possible.

[jimthedev]

@kwonoj I think it is possible assuming that they provide us some hook that we could wrap. I've not done much native node development so I'd probably reach out to community members on how to implement it, but as long as they implement the inquirer interface then I can see it being possible.

Thanks again for putting in this PR. RxJS is such a freaking awesome project.