When allowing multiple marks on a container, we renamed the "mark"
field to "marks". This breaks i3-save-tree which will now filter out
the marks on a window because it doesn't match anymore. This commit
fixes that issue.
Thanks to /u/xenomachina for hinting to this issue.
This allows "--workspace 3" for numbered workspaces, e.g., if the name is actually
"3:foo". This introduces the same functionality the IPC already offers in many places.
If no option is given, i3-save-tree should default to the currently focused workspace.
Specifying both --workspace and --output will still yield an error.
Orestis Floros