`pygmentize` 1.0+ has an `-N` option that attempts to match a file (via
the extension) to a language lexer. If `pygmentize` is installed, we'll
run it with this option to get a language.
If no language is detected, `pygmentize -N` returns `text`. In that case,
we'll first look for a user-provided language to use as a fallback. If no
language was provided, highlight using `ruby` as a reasonable default.
Closes issue #19.
This closes issue #10, in theory, but I'm not completely happy with the
behavior. The output for both UTF-8 and ISO-8859-1 sources is arguably
correct, but I think it'd be better to do some autodetecting of the file
encoding, and explicitly convert everything to UTF-8 on input. One
option is the [`chardet` gem][gem], but I'm loath to add another
dependency to Rocco...
[gem]: http://rubygems.org/gems/chardet/versions/0.9.0
