add install target to Makefile and corresponding prefix variable to config.mk

Merge branch 'master' into 31-independents-mouse-focus

make XWayland support optional

xwayland: unmanaged (dropdown menu) support

warn but don't error on unused function

sacrifice 24 lines to suckless style :)

turn on some warnings

move config.h to config.def.h

make Makefile a bit more my style

Start with tinywl

Add a config.h into which configurables can be moved.