doc: convert git-format-patch synopsis and options to new style

doc: convert git-format-patch synopsis and options to new style

Replace [verse] with [synopsis] in the SYNOPSIS block and remove
single-quote formatting from the command name.

Backtick-quote all option terms in the OPTIONS section, convert
standalone placeholders to _<placeholder>_ form, and convert
single-quoted commands and tools in prose to backtick form.

Also update the included files:
- diff-options.adoc: backtick-quote the git-format-patch-specific
  option terms (-p, --no-stat, --max-depth=<depth>)
- format-patch-caveats.adoc: convert patch(1) to `patch`(1)

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>