sfdisk: Improve the typesetting of the manual

sfdisk: Improve the typesetting of the manual

  FIXME
  Units KB, MB, GB, etc. are ambiguous (not necessarily used here)
  Prefixes kilo, mega, giga, etc. are ambiguous with the unit byte (ditto)

  Change ' \- ' to ' \(en ' (an en-dash), if it is a dash (pause,
separation)

  Change ' - ' to ' \(en ' (an en-dash), if it is a dash (pause,
separation)

  Change '\-' to '-' (code "hyphen-minus", rendered with the glyph
hyphen in troff), if it is a part of a compound name.
  A minus is not used in words.  People using UTF-8 and copy-and-paste
can(?) (may?) use "info", "man --ascii" or the command "man" should
have an option to display the '-' ("hyphen-minus") in names of options
with the code (character name) "hyphen-minus" (u002D) instead of
"u2010" (code (character) name "hyphen").

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

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

  Correct space between sentences to two space characters (or begin
each sentence on a new line).

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

  Add \~ (no-break space) around '|' (means "or")

  Change ' -- ' to ' \(en ' (an en-dash), if it is a dash (pause,
separation)

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