This PR adds multi-monitor support to ZWM and fixes the following bugs:
1- double free in split_string() which causes zwm to exit with SIGABRT as it starts up.
2- attempt to deference a null pointer when trying to delete a node in master layout, this leads to immediate crash.
This PR adds multi-monitor support to ZWM and fixes the following bugs: 1- double free in split_string() which causes zwm to exit with SIGABRT as it starts up. 2- attempt to deference a null pointer when trying to delete a node in master layout, this leads to immediate crash.