This use of *? was both incorrect and catastrophically backtracking
when embedding this regex into a larger regex with a trailing pattern,
since it could match much more than intended and try exponentially
many positions in that process.

This commit adds a new url field to a lexer, which can be used to link
to the language website, instead of relying on having the link in either
languages.rst or the docstring of the lexer. Additionally, it changes the
languages.rst file to auto-generate the list of lexers from the actual
source code, using the provided URL.