fix crash when setting a custom mode

rework outputmgrapplyortest()

first disable requested monitors, then enable and/or change mode, x and y, etc.
This is mostly what sway does

2200: let's use this wisely

Looks like [suckless-dev] was right about one thing.

fix dist target

use `git describe` to generate version

check client_from_wlr_surface() returning NULL in urgent()

fix #281

fix segfault if parent->mon is unset

use the layer surface to create popups

make sure we do not create a double fullscreen_bg

and also make sure we do not destroy it if it does not exist
Fixes: #274

conform the xdg-protocol with fullscreen translucent clients

see `setfullscreen()` for more info

always set the same monitor and tags for child clients of a client

fixes #272

do not focus clients if a layer surface is focused

force line-buffered stdout if stdout is not a tty

Revert "only call wlr_seat_keyboard_notify_enter() if a keyboard is found"

This reverts commit 8e03bce6217117f0687cd727ae2c47bdd3c0fe5a.
fixes #270

remove a useless check

if `s->role_data == NULL`, wlr_*_surface_from_wlr_surface() will return NULL
and we are checking it

Update README.md

only call wlr_seat_keyboard_notify_enter() if a keyboard is found

check pointer focus in arrange()

include DWLCFLAGS into linking step

arrange client's monitor if size has change since last commit