Replicates i3 option. Verbosity level given as command line argument
becomes default log level, and using 'debuglog toggle' switches back and
forth between default and debug (or L_ERROR and debug if default is also
L_DEBUG).
This is an undocumented feature (the word "number" is just ignored
anyway), but it exists to be compatible with i3 config syntax.
Plus some code cleanup at the same time.
In i3 the ipc reply will contain a human readable error message, and
this patch replicates that behaviour.
However, that error message is also useful for logging, which this
patch takes advantage of.
E.g. instead of logging errors directly in commands.c/checkargs, it is
fed back to the caller which eventually ends up logging everything with
maximum context available (config.c/read_config).
So instead of logging e.g. "Error on line 'exit'" it will now log:
"Error on line 'exit': Can't execute from config."
Before this patch sway would proceed into find_handler which would cause
a crash trying to parse a NULL string.
This could be triggered via e.g. `i3-msg -s $(sway --get-socketpath)`.
When using an i3 config verbatim in sway this switch to exec or
exec_always might appear.
Before this patch the switch would be passed to /bin/sh, causing
an error, and the command would not be run.