Adding Heatmap trace implementation

[eric-czech]

Hi @alexarchambault, thank you for your work on this project! I love how you've structured it.

I wanted to get more familiar with it by adding Heatmaps and I think this is a solid start. Let me know if I missed anything, but this PR includes:

• Additions to Trace.scala for Heatmaps
• Necessary changes in the argonaut codec class to support new parameters, namely colorscale serialization
• Examples in the Demo
• New tests in DocumentationTests to force decoding of all the Plot.ly heatmap examples

I also needed to make a few minor tweaks to the make-ghpages.sh script in order to test that the demos are still being rendered correctly.

Lastly, I also needed to update plotly-documentation to correct some errors in the JS examples. How would you suggest I commit that back to your fork? Here's the patch for the diff: plotly-documentation.patch.txt. There's not much to it beyond a typo and some parameters that are supposed to be on the main layout rather than an axis.

Thanks again!

[eric-czech]

FYI it looks like everything cleared on Travis except the plotly-documentation fixes I mentioned (not sure how to get them upstream for the build).

Also, I'd like to include a way to propagate nulls but they're being replaced somewhere in the encoding process. This might be better left to a separate PR/issue, but do you know off the top of your head how to make this work?

Heatmap(
    z=Seq(
        Seq(10, null.asInstanceOf[Int]), 
        Seq(10, null.asInstanceOf[Int])
    ),
    x=Seq("Yes", "No"),
    y=Seq("Morning", "Evening"),
).plot()

(The cells on the right should be blank instead of 0, like in https://plot.ly/javascript/heatmaps/#heatmap-with-categorical-axis-labels)

[alexarchambault]

Thanks a lot, that looks neat!

I just pushed a commit (alexarchambault/plotly-documentation@eae136b) in the fork of plotly-documentation used as a submodule here, based on your patch.

Check it out from the plotly-documentation directory, and add the updated submodule from the plotly-scala repo (something like cd plotly-documentation && git fetch origin && git checkout eae136b && cd .. && git add -- plotly-documentation should do). That ought to make the tests pass.

[alexarchambault]

About the nulls, I think they could be supported either by adding an extra conversion from Seq[Seq[Option[Int]]] (argonaut renders that as either integers or nulls IIRC), and / or adding a conversion from Seq[Seq[Integer]], which are fine with null values. In the former case, users would pass values like Seq(Seq(None, Some(2), Some(3))). In the latter case, they would pass Seq(Seq[Integer](null, 2, 3)) (explicit [Integer] required).

[eric-czech]

Awesome, thanks for committing that! That makes sense with the nulls too -- I may try to tackle that with one of those approaches if it starts to chafe a little more but for now I'll leave this PR as-is. Looks like it's all clear now.

[alexarchambault]

Merging, thanks @eric-czech!