feat(rule): add limit_to_rooms

[wass3r]

❤ THANKS FOR HELPING OUT :D

Proposed change

Per the story, this adds limit_to_rooms at a rule level which allows for use cases like having one bot service multiple rooms/channels differently.

Additionally, since the next release will have some breaking stuff already, I decided to add output_to_rooms to actions instead of replacing limit_to_rooms with it. Planning to remove in following release. Will update the docs to just reference output_to_rooms already though.

closes #113

Types of changes

What types of changes is this pull request introducing to flottbot? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

You can fill this out after creating your PR. Put an x in the boxes that apply

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[coveralls]

Pull Request Test Coverage Report for Build 1051612754

• 28 of 28 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.6%) to 36.0%

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Totals
Change from base Build 1050444848:	0.6%
Covered Lines:	873
Relevant Lines:	2425

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💛 - Coveralls