Evaluate J through emacs dynamic modules and ~libj.so~.

I wrote this for fun and because I was getting fed up with how j-mode
and org-babel interact. The code right now is usable for me but there
are many ways it sucks, so I'd caution others against using it.

* Lowlights
- *J->emacs* & *emacs->J*: marshall data between J and emacs.
- *calculator*: access J prompt in the mini bar through key binding
  <kbd>M-j</kbd>.
- *viewmat*: if the ~viewmat.png~ file changes from executing some J, a
  buffer pops up to display it inside emacs.
- *plot*: if the ~plot.pdf~ file changes from executing some J, the
  buffer is opened and viewed through ~pdf-tools~.
- *ob-jpl*: facilities for using ~jpl-mode~ in org mode.
- *joogle*: emacs procedure that prompts for a J token and opens the
  corresponding NuVoc page in a browser.
- *font lock*: correctly classifies J tokens by verb, adverb,
  conjunction, and so on (j-mode misidentifies things like ~:~ and a
  few others) and adds a colors for nouns and names. Basically, with
  ~for_a. i. 10 do.~ font-lock will recognize that ~a~ is a binding
  and color it, bindings such as ~\'a b\'=. y~ don't get highlighted
  as strings, and things like ~a:~ and ~a.~ get their own color.
- *pretty symbols*: approximate J in APL glyphs through <kbd>M-p</kbd>
  and pretty symbol mode.

* Warnings
- Using J in this way can cause segfaults (wip)!