Implement allowNull options to @turf/meta fixes #946

[DenisCarriere]

Implements: #946
Ref Issues: #940

JS Example

var features = turf.featureCollection([
  turf.point([26, 37], {foo: 'bar'}),
  turf.point([36, 53], {hello: 'world'}),
  turf.feature(null)
]);

turf.featureEach(features, {allowNull: false}, feature => {
  // Callbacks 2 features
});

turf.featureEach(features, {allowNull: true}, feature => {
  // Callbacks 3 features
});

// Backwards compatible with TurfJS v4.0
// allowNull defaults to `false`
// most common errors in TurfJS are related to null geometries being contained in FeatureCollections
turf.featureEach(features, feature => {
  // Callbacks 2 features
});

Up for debate

allowNull currently defaults to false, there could be an argument to set this default as true. My personal preference is allowNull=false.

[stebogit]

@DenisCarriere I'll just comment only on this one but it applies to the other method as well.
The tests you put in place will certainly prove me wrong, but how can this

turf.featureEach(features, {allowNull: false}, feature => {
  // Callbacks 2 features
});

be backward compatible and not breaking code based on the current version?

I thought this would have been the right order:

turf.featureEach(features, feature => {
  // Callbacks 2 features
}, {allowNull: false});

I'm probably missing something here.

[DenisCarriere]

@stebogit Agreed it's a bit confusing having options, it's even more confusing when handling featureReduce since if the options are defined after the callback it's in the same position as the initialValue which is defined as any value.

🤔 I think I'm just going to drop this PR... no options in all of these Array.map & Array.reduce typed methods.

[DenisCarriere]

Going to close this PR, doing this I found a few issues in the tests, I'm going a new PR related to only changes related to the test.js