extend toBeEmpty to support Map, Set, and any other iterable

[moredip]

What

Teach toBeEmpty how to test for emptiness of any Iterable.

Why

Implements #158. Adds support for testing emptiness of Map and Set, amongst others.

Notes

@mattphillips suggested implementing this using [...value].length === 0. That would have been a neat, terse implementation but would not have worked for non-terminating iterables (which admittedly is a pretty obscure edge case). A more plausible advantage of not using the destructuring approach is that we avoid unecessary evaluation of potentially large/expensive iterables - we only need to go as far as yielding one value. Not really a huge deal either way, but it seemed a good tradeoff to make the implementation a bit bigger in exchange for supporting weird custom iterables.

Housekeeping

• Unit tests
• Documentation is up to date
• No additional lint warnings
• Add yourself to contributors list (yarn contributor)
• Typescript definitions are added/updated where relevant

[codecov-io]

Codecov Report

Merging #160 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #160   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files         103    103           
  Lines         500    505    +5     
  Branches       85     86    +1     
=====================================
+ Hits          500    505    +5

Impacted Files	Coverage Δ
src/matchers/toBeEmpty/predicate.js	100% <100%> (ø)	⬆️

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[benjaminkay93]

i like this alot, wd!

[mattphillips]

@moredip sorry for the delay in getting this merged! Looks great thanks 👍