Vega-lite: Add more concat / repeat examples to the gallery

[kanitw]

Right now we only have one example listed, but there are actually many good examples in the documentation.

[ydlamba]

How about adding a repeated histogram (vertically) to example gallery? https://vega.github.io/vega-lite/docs/repeat.html#example-repeated-histogram

[kanitw]

I think we should add all examples in the concat and repeat pages except for SPLOM, we can just link to interactive one.

(We should also add a note to https://vega.github.io/vega-lite/docs/repeat.html#example-scatterplot-matrix-splom to say that there is an interactive version too.)

[ydlamba]

In concat docs, the same example is displayed first horizontally and then vertically. Should we add both to the gallery or just one of them?
In my opinion, adding only one of them will work.

[kanitw]

One is fine I guess. :)

[ydlamba]

Can I work on this?

[kanitw]

Definitely!

For any small issue, feel free to comment the issue that "I would like to work on this" so that we and other people know that you will work on it.

For larger issue that involves syntax or rule design, also feel free to comment to propose a design (or even better a few designs) first before going to implement them. This way will help reduce the development time required.