Tooltips - revisited about altair

[AliciaSchep]

I think these changes will make for a nicer api in terms of where to specify the tooltip (in the encodings & vegalite spec)... too bad they didn't come a bit earlier though!

[ijlyttle]

I agree with both of your assertions!

Because we will be able to create tooltips using Altiar, I don't think that the current tooltip-constructor functions will belong in this R package. I think that this package should focus on a clean interface to Altair, and embedding, or otherwise communicating the resulting charts.

That being said, I like the idea of using piping to construct a custom tooltip, so I am thinking to start a companion package altools, where we could build R-like helpers. The altair package could suggest altools.

[ijlyttle]

Before removing the tooltip functions, I made this block so I could remind myself of what I liked and thought could be improved in the "old" way.

[ijlyttle]

Leaving this open as a reminder to rebuild tooltip-functions, either here or in altools. Moving the "demolition" aspects to #45.

[ijlyttle]

I think this is solved; the tooltips in the latest Altair seem to work as we might expect.