Hi All,

This is a small set of patches to add a bit more information to the messages
emitted in the course of babel evaluation. Specifically about
⁃ What type of element is responsible for the evaluation (source block, babel call,
  inline source)
⁃ Where the element is (if no name is set)
⁃ How long evaluation took

For example, previously `C-c C-c' on a babel call would have produced a message
like this:
┌────
│ executing Emacs-Lisp code block...
│ Code block evaluation complete.
└────
and now this might look like so:
┌────
│ executing Emacs-Lisp call on line 143...
│ Code block evaluation complete (took 0.2s).
└────

I think this is a pretty sensible change, but feedback is always nice.

If there are no objections, I expect I’ll merge this in a few days.

All the best,
Timothy