- Improved support for custom macro definitions.
- LinePart type has been added. RoffStr is now one
constructor of LinePart (the other being MacroArg).
- MComment has lost its argument.
- MEndMacro has been removed.
- MStr has been removed (we now simply use LinePart).
- Macros now store a list of tokens.
- Each macro argument is a [LinePart], instead of a LinePart.
- .BR now behaves as documented in man (and doesn't create a link).
This should just add to metadata (title, date, section),
and not produce a level-1 header. (That might be done
in the template, depending on the output format.)