This removes our last dependency on Xlib! :)
(Okay, an Xlib dependency still comes in through other libraries that we
link against, but it’s not us. Our code is simpler by this change and
uses one less connection to X11.)
This adds some code duplication which we might remove in a future
refactoring or not. Depends on whether unifying the parsers actually
makes the code better or not. I suspect it doesn’t :-).
CPPFLGES, CFLAGS and LDFLAGS should be user variables
We now provide default flags but use I3_*FLAGS flags for our own needed
flags
Also reoder lib flags a bit
Michael Stapelberg