Rewrote to use useField hook and provide useFieldArray hook

[erikras]

Also migrated all tests to 🐐 React Testing Library.

Similar to final-form/react-final-form#467.

Fixes #77.

[codecov]

Codecov Report

Merging #80 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #80   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      6    +3     
  Lines          75     58   -17     
  Branches       17     10    -7     
=====================================
- Hits           75     58   -17

Impacted Files	Coverage Δ
src/defaultIsEqual.js	100% <100%> (ø)
src/FieldArray.js	100% <100%> (ø)	⬆️
src/useConstant.js	100% <100%> (ø)
src/renderComponent.js	100% <100%> (ø)	⬆️
src/useFieldArray.js	100% <100%> (ø)
src/testUtils.js	100% <100%> (ø)

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[erikras]

Published in v3.0.0.