[O] Bug: Incorrect/incomplete documentation for org-timestamp-change

[Tim Landscheidt]

I wanted to (and did) change a number of timestamps by a
constant.  So I found (and successfully used)
org-timestamp-change which starts with (master):

| […]
| (defun org-timestamp-change (n &optional what updown suppress-tmp-delay)
|   "Change the date in the time stamp at point.
| The date will be changed by N times WHAT.  WHAT can be `day', `month',
| `year', `minute', `second'.  If WHAT is not given, the cursor position
| in the timestamp determines what will be changed.
| When SUPPRESS-TMP-DELAY is non-nil, suppress delays like \"--2d\"."
| […]

Incorrect is the enumeration of valid values for WHAT: 'hour
is missing and 'second is probably wrong (?).

Incomplete is the documentation for UPDOWN: I had assumed it
was the "direction" of change, but that is determined in-
stead by the sign of N.