partx: Improve the typesetting of the manual

partx: Improve the typesetting of the manual

  Add a space character around '|' (means "or")

  Add "(hyphen-minus)" after "\-" to show character name for input

  Change '\-\-' to '\en', when it is used as a dash (pause, separation)

  Add a comma before "or" in a series of words (3 or more)

  Change '-' to '\(en' (an en-dash), if it means a range

  Protect a full stop (.), that begins or ends a string, with \&

  Change '--' to '\-\-', if it indicates an option

  Change '-' to '\-', if it indicates an option

  Change '-' to '\-', if means a minus

Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>