Documentation/rev-list-options.txt: fix some grammatical issues and typos

Documentation/rev-list-options.txt: fix some grammatical issues and typos

Various fixes:

 - fix typos (e.g. "show" -> "shown")
 - use "regular expression(s)" instead of "regexp" where appropriate
 - reword some sentences for easier reading
 - fix/improve some grammatical issues (e.g. comma usage)
 - add missing articles (e.g. "the")
 - change "E-mail" to "email"

Signed-off-by: Jason St. John <jstjohn@purdue.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>