sway-bar(5) documents `modifier none`, which comes from i3. This
implements the functionality for `modifier none` since it was not
previously implemented. The bar modifier toggles visibility of the bar
when the bar mode is set to hide. When the bar modifier is set to
`none`, the ability to toggle visibility of the bar will be disabled.
Modifier handling functions were moved into sway/input/keyboard.c;
opposite_direction for enum wlr_direction into sway/tree/output.c;
and get_parent_pid into sway/tree/root.c .
This commit mostly duplicates the wlr_log functions, although
with a sway_* prefix. (This is very similar to PR #2009.)
However, the logging function no longer needs to be replaceable,
so sway_log_init's second argument is used to set the exit
callback for sway_abort.
wlr_log_init is still invoked in sway/main.c
This commit makes it easier to remove the wlroots dependency for
the helper programs swaymsg, swaybg, swaybar, and swaynag.
Patch tested by compiling with `__attribute__ ((format (printf, 2, 3)))`
applied to `cmd_results_new`.
String usage constants have been converted from pointers to arrays when
encountered. General handler format strings were sometimes modified to
include the old input string, especially for unknown command errors.
