Rename fQS -> fqs
Make sens_params optional; update doc
Specify OCaml's C header path
Fix MathJax handling in configure

- The wording must be clear if MATHJAX is to be set to the directory
  containing MathJax.js, or to MathJax.js itself.

- The presence of URI schemes besides file:// doesn't imply that it's
  remote.

- mathjax should not be set during the argument processing loop, for
  otherwise we can't detect if MATHJAX_PATH was explicitly supplied at
  all.
Remove handling of file:// schemes for MathJax

Handling hosts is too tricky for a shell script, and given that the
example in --help now says /usr/share/javascript/mathjax, no one in the
right mind will specify a file:// anyway.