wip: map key combos to custom text strings (including escapes)

With this, it is now possible to map key combos to custom escapes. The
new bindings are defined in a new section, “text-bindings”, on the
form “string=key combo”.

The string can consist of printable characters, or \xNN style hex
digits:

  [text-bindings]
  abcd = Control+a
  \x1b[A = Control+b Control+c Control+d  # map ctrl+b/c/d to UP

config.h

@@ -47,6 +47,7 @@ struct argv {
 enum binding_aux_type {
     BINDING_AUX_NONE,
     BINDING_AUX_PIPE,
+    BINDING_AUX_TEXT,
 };
 
 struct binding_aux {
@@ -55,6 +56,11 @@ struct binding_aux {
 
     union {
         struct argv pipe;
+
+        struct {
+            uint8_t *data;
+            size_t len;
+        } text;
     };
 };
 
@@ -63,6 +69,11 @@ enum key_binding_type {
     MOUSE_BINDING,
 };
 
+struct config_key_binding_text {
+    char *text;
+    bool master_copy;
+};
+
 struct config_key_binding {
     int action;  /* One of the varios bind_action_* enums from wayland.h */
     struct config_key_modifiers modifiers;