Impliment i3-style marks

This commit adds three commands to sway: `show_marks`, `mark` and
`unmark`. Marks are displayed right-aligned in the window border as i3
does. Marks may be found using criteria.

Fixes #1007

1 files changed, 5 insertions, 0 deletions

diff --git a/include/sway/container.h b/include/sway/container.h
index 46925589..37192ce3 100644
--- a/include/sway/container.h
+++ b/include/sway/container.h
@@ -165,6 +165,11 @@ struct sway_container {
          * Number of slave groups (e.g. columns) in auto layouts.
          */
         size_t nb_slave_groups;
+
+        /**
+         * Marks applied to the container, list_t of char*.
+         */
+        list_t *marks;
 };
 
 enum visibility_mask {