Documentation/rev-list-options: wrap --date=<format> block with "--"

Using "+" to continue multiple list items is more tedious and
error-prone than wrapping the entire block with "--" block markers.

When using asciidoctor, the list items after the --date=iso list items
are incorrectly formatted when using "+" continuation.  Use "--" block
markers to correctly format the block.

When using asciidoc there is no change in how the content is rendered.

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -805,12 +805,13 @@ include::pretty-options.txt[]
 	author's). If `-local` is appended to the format (e.g.,
 	`iso-local`), the user's local time zone is used instead.
 +
+--
 `--date=relative` shows dates relative to the current time,
 e.g. ``2 hours ago''. The `-local` option has no effect for
 `--date=relative`.
-+
+
 `--date=local` is an alias for `--date=default-local`.
-+
+
 `--date=iso` (or `--date=iso8601`) shows timestamps in a ISO 8601-like format.
 The differences to the strict ISO 8601 format are:
 
@@ -818,15 +819,14 @@ The differences to the strict ISO 8601 format are:
 	- a space between time and time zone
 	- no colon between hours and minutes of the time zone
 
-+
 `--date=iso-strict` (or `--date=iso8601-strict`) shows timestamps in strict
 ISO 8601 format.
-+
+
 `--date=rfc` (or `--date=rfc2822`) shows timestamps in RFC 2822
 format, often found in email messages.
-+
+
 `--date=short` shows only the date, but not the time, in `YYYY-MM-DD` format.
-+
+
 `--date=raw` shows the date as seconds since the epoch (1970-01-01
 00:00:00 UTC), followed by a space, and then the timezone as an offset
 from UTC (a `+` or `-` with four digits; the first two are hours, and
@@ -835,28 +835,28 @@ with `strftime("%s %z")`).
 Note that the `-local` option does not affect the seconds-since-epoch
 value (which is always measured in UTC), but does switch the accompanying
 timezone value.
-+
+
 `--date=human` shows the timezone if the timezone does not match the
 current time-zone, and doesn't print the whole date if that matches
 (ie skip printing year for dates that are "this year", but also skip
 the whole date itself if it's in the last few days and we can just say
 what weekday it was).  For older dates the hour and minute is also
 omitted.
-+
+
 `--date=unix` shows the date as a Unix epoch timestamp (seconds since
 1970).  As with `--raw`, this is always in UTC and therefore `-local`
 has no effect.
-+
+
 `--date=format:...` feeds the format `...` to your system `strftime`,
 except for %z and %Z, which are handled internally.
 Use `--date=format:%c` to show the date in your system locale's
 preferred format.  See the `strftime` manual for a complete list of
 format placeholders. When using `-local`, the correct syntax is
 `--date=format-local:...`.
-+
+
 `--date=default` is the default format, and is similar to
 `--date=rfc2822`, with a few exceptions:
-
+--
 	- there is no comma after the day-of-week
 
 	- the time zone is omitted when the local time zone is used