Escape LaTeX characters in conf.py

[evangoer]

For most of the fields you can set for sffms in conf.py, the software should be escaping LaTeX characters. A few power-user fields (such as sffms_msheader) should NOT have LaTeX escaping.

1. Add LaTeX escaping to most sffms conf.py fields.
2. Make it clear in the docs which fields are not escaped.
3. Provide a config option to turn off LaTeX escaping in conf values.

[evangoer]

And try using sphinx.util.texescape, it's probably much better than what we're using currently.