Add the option allow-empty-functions in no-empty

[markvincze]

PR checklist

• Addresses an existing issue: empty-block report about empty functions #2107
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Introduces option to allow function declarations to be empty while using no-empty.

Is there anything you'd like reviewers to focus on?

This is my first PR to tslint, so any feedback is welcome.
I was a bit unsure if I did the correct setup for the options property (an array with an anyOf of the two strings).

CHANGELOG.md entry:

[enhancement] Introduces option to allow function declarations to be empty while using no-empty.

[palantirtech]

Thanks for your interest in palantir/tslint, @markvincze! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[markvincze]

I signed the CLA.

[ikokostya]

Any updates?

[markvincze]

@ikokostya,
To me it seems that tslint is not actively maintained at the moment. PRs are piling up without getting reviews or getting merged.
I've tried to ping @tslint on Twitter too, but no response.

[johnwiseheart]

Hello everyone- tslint has recently gotten some new maintainers - myself as one of them. Unfortunately it’s taking us a while to ramp up on everything and get through all the issues, but we’re starting to merge things in and try to bring tslint back to a stable state. Hold tight, we’ll get to this PR as soon as we can.

[markvincze]

Hey @johnwiseheart, great news!

[suchanlee]

it looks good to me, thanks @markvincze!