rev-parse(1): logically group options

rev-parse(1): logically group options

The options section of the git-rev-parse manual page has grown
organically so that there now does not seem to be much logic behind the
ordering of the options.  It also does not make it clear that certain
options must appear first on the command line.

Address this by reorganising the options into groups with subheadings.
The text of option descriptions does not change.

Signed-off-by: John Keeping <redacted>
Signed-off-by: Junio C Hamano <redacted>