[WIP] add documentation for onRequestClose function

[alaskaa]

Hey 👋

First of all, thank you for such a great library - it worked beautifully for my usecase and I found it very straightforward to use.

I've noticed you didn't very openly advocate the inbuilt function "onRequestClose" and therefore thought it would be awesome to add it to the docs.

I discovered it more or less by accident, and it provided me with the opportunity to leave the modal and return to a previous modal which was very useful. Happy to rework the PR or add the info at another stage, but I think it would be awesome if it is documented somehow that it can be used to close the dropdowns or modals!

[coveralls]

Pull Request Test Coverage Report for Build 64

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 81.538%

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Totals
Change from base Build 63:	0.0%
Covered Lines:	24
Relevant Lines:	24

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💛 - Coveralls

[codecov-io]

Codecov Report

Merging #32 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #32   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines          24     24           
=====================================
  Hits           24     24

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[jasonleibowitz]

@alaskaa Apologies for the delayed response. This is a great call out. Thanks for the PR!