explainST: HTML format should emit chunks

[dylanbeaudette]

Also, how can we encode spacing to match font size of subgroup taxa? SVG output is likely the best route here.

[brownag]

For "emit chunks" is this to allow for vector input of taxon names and list output of HTML? i.e. same as lapply(taxa, explainST, format="html")? Currently we don't support multiple taxa on the same HTML page or in text output without manually iterating.

I believe the spacing issue was resolved using div styles with monospace font family.

SVG output might be useful but not sure where I would use it.