bump version to 0.5

Merge remote-tracking branch 'upstream/main' into wlroots-next

allow specify DATADIR (to install desktop file)

Merge remote-tracking branch 'upstream/main' into wlroots-next

bump version to 0.4

remove `--long` from git-describe command

Merge branch 'main' into wlroots-next

bump version to 0.4-rc3

Merge remote-tracking branch 'upstream/main' into wlroots-next

bump version to 0.4-rc2

Merge remote-tracking branch 'upstream/main' into wlroots-next

bump version to 0.4-rc1

Merge branch 'wlroots-next' into main

Merge remote-tracking branch 'djpohly/main' into wlroots-next

rework Makefile

- allow user to use a different pkg-config binary
- restore almost all (and add other ones) warning flags (-Werror is not set)
- $(XWAYLAND) is added to our CPPFLAGS
- remove useless comments
- don't generate idle-protocol.h (not used)

add missing library (xcb-icccm)

this library is also used by wlroots, so nothing new

append `-dev` to $(_VERSION) (should have added it a long time ago)

Merge remote-tracking branch 'djpohly/main' into wlroots-next

use `git describe` to generate version

include xcb only when building with xwayland support