Reset the state of the component and its inputs when a different props.value is passed in

[acusti]

note that this branch was branched off of #154 and will be easier to review in isolation from those changes.

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this PR simplifies component state handling and updates state.value and state.input when props.value changes to enable resetting the component’s state as requested in #129 (also provides a better solution for #69). it also adds fallbacks and checks to work with props.value being null or undefined. these changes enable the following pattern, which i added as a new “With Reset” story to the docs:

function Resettable() {
    const [value, setValue] = React.useState(null);

    return (
        <Fragment>
          <ReactCodeInput onChange={() => setValue(null)} value={value} />
            <button onClick={() => setValue('')}>Reset</button>
        </Fragment>
    );
}

commits are atomic and explain in detail what changes are contained in the PR.

[codecov[bot]]

Codecov Report

Merging #155 (3593aa9) into master (2599c5d) will increase coverage by 0.44%. The diff coverage is n/a.

:exclamation: Current head 3593aa9 differs from pull request most recent head 61d697e. Consider uploading reports for the commit 61d697e to get more accurate results

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
+ Coverage   96.55%   96.99%   +0.44%     
==========================================
  Files           2        2              
  Lines         145      133      -12     
  Branches       41       36       -5     
==========================================
- Hits          140      129      -11     
+ Misses          5        4       -1     

Impacted Files	Coverage Δ
src/utils.js
src/ReactCodeInput.js
ReactCodeInput.js	96.72% <0.00%> (ø)
utils.js	100.00% <0.00%> (ø)

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