Create layers based on a list of features.

[manthey]

Currently, if you want to use a feature, you need to know what renderers in works in and manually check if those renderers are available on the current platform. If the renderer isn't available, we fall back to the null renderer, which is only useful for the tile layers.

With this change, you can ask for a new layer based on the features you want. If there are any renderers available that support all of the listed features, that renderer will be used. Furthermore, there is now an inherent preference in renderers in the order vgl -> canvas -> d3 -> null, so we'll fall back to a better renderer than the null renderer in many instances.

Features can have capabilities. For instance, the quad feature is only fully implemented in the vgl renderer. Image quads are mostly implemented in the d3 and canvas renderers (when the quad is a parallelogram). Color quads are implemented in the d3 renderer. If you ask for a layer that supports {features: ['quad']}, you could get any of the vgl, d3, or canvas renderers (based on the support of that renderer). If you ask for {features: ['quad.clr']}, you will only get either the vgl or d3 renderer. If you ask for {features: ['quad.img-full']}, only vgl will do.

Many examples have been updated to use this. This means that some examples will now work on more platforms (since they would only work if you have vgl, but now will work in other cases).

[codecov-io]

Current coverage is 76.42%

Merging #590 into master will increase coverage by 0.19%

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+ Hits           5503       5559    +56   
+ Misses         1716       1715     -1   
  Partials          0          0          

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[aashish24]

🎉 will complete my review tomorrow but I liked what I reviewed so far

[aashish24]

+1

[aashish24]

Mostly looks great 😋 to me but I have one suggestion for discussions.

[aashish24]

LGTM 🎉

[aashish24]

@manthey should we go ahead and merge it?

[jbeezley]

LGTM