Customization: captions above instead of below in some blocks

[InThisStyle10s6p]

This relates somewhat to #84 and #174. It would be convenient to have the option to specify and render captions above rather than below certain blocks (this might be handy with code blocks and figures, too). I don't see a way to do this currently.

For instance, it would be nice to have the following

<div id="thm:algebra">
Fundamental theorem of algebra.

Any non-constant complex polynomial has a root.
</div>

be rendered as, say,

<div id="thm:algebra">
Theorem 1: Fundamental theorem of algebra.

Any non-constant complex polynomial has a root.
</div>

Perhaps in the custom prefix definition there could be a surtitle: true option that would trigger this behaviour?

[lierdakil]

Sounds reasonable. I'll see what I can do.