gui/create-item: add --multi to option list in docs, remove --all (no effect)

Author: lethosor

docs/gui/create-item.rst

@@ -37,6 +37,8 @@ Examples
 Options
 -------
 
+``--multi``
+    Also prompt for the quantity of items to create.
 ``--unit <id>``
     Use the specified unit as the "creator" of the generated item instead of the
     selected unit.

gui/create-item.lua

@@ -249,7 +249,6 @@ utils=require('utils')
 
 validArgs = utils.invert({
  'startup',
- 'all',
  'restrictive',
  'unit',
  'multi'