Split debug messages from ordinary run

Need to pass debug arguments (or simply `make debug` in order to enable
debug messages).
Add X resources support

User configuration now takes place mostly in the Xresources file.
Default configuration is defined in karuibar.h (maybe is going to be
moved elsewhere one day).
Fix handling of escape character length

We assume it's of length 6, but check afterwards to be sure.
Add battery module

Currently the paths for looking up battery stats are hardcoded, but will
be moved away once Xresources is handled more elegantly.