Get rid of isValidElement and Children

[molefrog]

Why? because these methods are not provided by Preact and can be replaced with more simplified versions.

isValidElement is replaced with element && element.props.

// preact
element && ((element instanceof VNode) || element.$$typeof===REACT_ELEMENT_TYPE)

// react
typeof object === 'object' && object !== null && object.$$typeof === REACT_ELEMENT_TYPE

React's Children iteration supports things like generators, edge cases like falsey children etc.

[codecov-io]

Codecov Report

Merging #27 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
- Coverage   98.42%   98.41%   -0.02%     
==========================================
  Files           5        5              
  Lines         127      126       -1     
  Branches       26       24       -2     
==========================================
- Hits          125      124       -1     
  Misses          2        2

Impacted Files	Coverage Δ
index.js	100% <100%> (ø)	⬆️

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[molefrog]

After a discussion with @StrayFromThePath we have decided to keep isValidElement method and provide an implementation for Preact, since the hack didn't seem to be secure.

Closing this and moving to #30