Document the purpose of `--file-directives` and `--no-pragmas`

[sgraf812]

I was browsing through the --help message of lhs2TeX and the explanations for the above flags raised more questions than they answered.

I was hoping that --file-directives would introduce some LINE pragmas that would allow pdflatex to map errors back to the location in .lhs files, but apparently such functionality might not even exist in the TeX world.

[kosmikus]

Re --file-directives, probably the best explanation is in the original commit message:

commit b05d65eda1613b2e9d855ef6f17807efa81b5854
Author: andres <andres@d54a9f6e-e2dc-0310-8252-bfaaff2a01be>
Date:   Sat Dec 31 16:58:31 2005 +0000

    * added an option --file-directives, which adds directives of the form

      %file <lineno> <filename>

      to the output files. This feature was suggested by Stefan Wehr, who also provided
      a patch. This implementation is different, though, and also produces slightly
      different results.

      The information in the result file can be used to produce better (TeX) error
      messages. Stefan Wehr has a tool for this.

So yes, it's for error messages, but no, it's not easy to use from normal LaTeX, at least not to my knowledge.

--no-pragmas should be mostly self-explanatory though?