Improve org-babel `rdfpuml-block`

[johanwk]

• [x] Make a defun that the block calls. Easier to debug, for one thing.
• [x] Use org-mode temporary directory
• [x] Replace sed and wc calls with Emacs commands in temporary buffer (these are typically not available on Windows)
• [x] Use a defcustom user option: if rdfpuml is available as an executable, use that, otherwise call with Perl
• [x] Replace uses of the f library with built-in file commands
• [x] Consider changing or replacing addtext, addtextend
• [x] Write prefixes from table prefix-table to file prefixes.ttl which is read by rdfpuml (needed ?)
• [x] allow for puml:options header argument

all in all, complete rewrite!

[johanwk]

This should be OK as of f23c2dc. There's an example in pizza.org

In the org file,

#+call: rdfpuml-block(ttlblock="pizza-construct")

#+RESULTS:
[[file:./images/pizza-construct.svg]]