Add hold 'action' to the "n" macro and ws-trim all "n" macro args
* lisp/org-macro.el (org-macro--counter-increment): Rename the
optional arg RESET to ACTION, as now that action can mean setting,
resetting or even holding the specified counter. ACTION set to
"-" will hold the previous value of the counter. White-space is
now trimmed from the NAME arg too.
* doc/org.texi (Macro replacement): Document the new hold action.
* testing/lisp/test-org-macro.el (test-org-macro/n): Add new tests for
the hold action.