Add Support for Roman, Sans Serif and Monotype fonts to LaTeX Formatter (patch)

Issue #334 resolved
created an issue

I made some minor changes to to create three new style options: roman, sans and mono which correspond to LaTeX's \textrm{}, \textsf{} and \texttt{} commands. I have implemented these in, this could also be implemented in some of the other formatters of course.

This would be beneficial for people who needed to pubish in black and white, but also adds more styling options for colour documents. You can combine colours, fonts and styles so you can have bold mono underline and a colour if you wanted to.

This doesn't seem to break anything, and all the tests pass after making these modifications (although I didn't see any tests specifically relating to styles or style directive parsing).