long vs wide form data

[Antonio Piccolboni]

The original goal was to accept data in both forms, seamlessly. Not sure much of that happened. Since officially altair likes the long form, the idea was to convert the data accordingly. It turns out that there are situations where wide is better and converting from long to wide requires an id column, in general, that was never introduced in the API.

1. Review the API to see if it supports long and wide data equally well
2. Review which functions support which
3. See what it would take to make the support both