XWayland still buggy, disable by default

consolidate some of the ugliness into a separate file

Similar to Linux kernel approach, encapsulate some of the uglier
conditional compilation into inline functions in header files.

The goal is to make dwl.c more attractive to people who embrace the
suckless philosophy - simple, short, hackable, and easy to understand.
We want dwm users to feel comfortable here, not scare them off.  Plus,
if we do this right, the main dwl.c code should require only minimal
changes once XWayland is no longer a necessary evil.

According to `cloc`, this also brings dwl.c down below 2000 lines of
non-blank, non-comment code.

let's not alienate the dwm folks

Fix style.

Merge pull request #65 from Keating950/master

Add install target to Makefile

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

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

Merge pull request #1 from djpohly/master

Pull Request

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

Merge branch 'master' into 24-xwayland-cursor

make XWayland support optional