Add link rel prev/next elements. Closes #66.
When Pygments lacks lexer, use "text" don't error.
New way to run Pygments.

Previously we started and waited 1 second -- which might be longer than
necessary, or not long enough.

Instead: Go ahead and start it running as part of module load, then wait
for it to print "Ready" message. Keep it running until Frog exits.
Be consistent about default fallback.

Always use `(pre () (code () ,x)).
Merge branch 'pyg-pipe-2'

Better way to start and run Pygments.