Allow assign to output

Implements the "assign" part of issue #2764.

parser-specs/config.spec

@@ -141,7 +141,7 @@ state FOR_WINDOW_COMMAND:
   command = string
       -> call cfg_for_window($command)
 
-# assign <criteria> [→] workspace
+# assign <criteria> [→] [workspace | output] <name>
 state ASSIGN:
   '['
       -> call cfg_criteria_init(ASSIGN_WORKSPACE); CRITERIA
@@ -149,6 +149,8 @@ state ASSIGN:
 state ASSIGN_WORKSPACE:
   '→'
       ->
+  'output'
+      -> ASSIGN_OUTPUT
   'workspace'
       ->
   'number'
@@ -156,6 +158,10 @@ state ASSIGN_WORKSPACE:
   workspace = string
       -> call cfg_assign($workspace, 0)
 
+state ASSIGN_OUTPUT:
+  output = string
+      -> call cfg_assign_output($output)
+
 state ASSIGN_WORKSPACE_NUMBER:
   number = string
       -> call cfg_assign($number, 1)