Figure embedding variants

[mgajda]

I have added mode="..." parameter per figure block:

• mode="floating" is default mode as before
• mode="column" creates minipage environment with a width of a single line, for narrow figures in multi-column mode (LaTeX only)
• mode="inline" strips the figure and caption to make the figure inline (all modes)
• mode="wrapped" uses wrapfig environment to wrap text around figure (LaTeX only)

[LaurentRDC]

I consider these new features to be out-of-scope. pandoc-plot transforms code blocks into image blocks; further formatting of image blocks should be done in another filter.

It is especially telling that two of the four options above are latex-only

[mgajda]

1. Initially LaTeX-only, since wrapping figures in HTML seems more difficult.
2. The problem with doing it in another filter is that it would depend on exact output format of pandoc-plot. That would make resulting code fragile.
3. If we want to only produce image blocks, then at least we should support inline option that strips the figure headers and produces an inline image.

[LaurentRDC]

This PR add functionality which is strictly out-of-scope.

it would depend on exact output format of pandoc-plot

All Pandoc filters share the exact same output format -- a JSON stream with a very specific structure.

[mgajda]

Since I do not feel like writing another plugin that parses pandoc-plot image block and reformats it in different way, I will maintain this branch in my own repo.

Unless there appears another filter that offers the functionality.