Adding Tableau Viz to dashboard extensions

[d45]

@filippostableau @johnDance @seanmakesgames @Kovner @alicemhsiao

Added two new topics:

• trex_tableau_viz.md - How to add Tableau Viz to a dashboard extension; Tableau Viz error messages
• trex_tableau_viz_ref.md - Reference information about what goes into the inputSpec parameter for the createVizImageAsync method; options for encoding, etc.

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Updates:

• Added Tableau Viz to the Release Notes (What's New)
• Fixed broken link (and error) about the existence of an XSD for the .trex file (trex_create.md)
• Updated _config.yml - gems deprecated and replaced by plugins

[johnDance]

Here is a meta comment: This is really the first time that an API is documented outside of the normal documentation. Should the trex_tableau_viz_ref.md be merged into the normal documentation for createVizImageAsync?

I think we should think about that. If we decide that this should be documented externally, then the main documentation should at least reference this.

[d45]

@alicemhsiao @johnDance - in the Tableau Viz reference page (trex_tableau_viz_ref.html), there is a section called "JSON specification for the inputSpec". And the example shown uses JSON formatting. I was thinking of dropping the JSON and changing this section to "Specification for the inputSpec"

Do we want to change the JSON example so that the example doesn't quote the keys ("mark", "description", "encoding", etc.)? I'm not sure if we will confuse developers about whether they need to create a JSON formatted object, or a JavaScript one? The both work (createVizImageAsync() doesn't care) since we convert JS script to JSON anyway. What do you think? Thanks.

[johnDance]

It is an object, so it should behave and be described as an object. I like your idea of dropping JSON. And yes, our example should remove the quotes from the keys.

Good ideas all around. Thanks!

[d45]

Thanks, John. Revised the reference page to refer to a JavaScript object, rather than a JSON one.