Due to lots of cases which were added and added to tree_move(), the function
was not really easy to understand. For this refactoring, I wrote tree_move()
from scratch, thinking about (hopefully) all cases. The testsuite still passes.
The move command also has different parameters now. Instead of the hard to
understand 'before v' stuff, we use 'move [left|right|up|down]'.
The welcome message is displayed using xmessage(1), not using your
terminal. Thus, it makes no sense to have this option anymore. Also,
the new lex/yacc parser cannot correctly handle the situation:
normal variables are expanded before parsing the file. As a replacement,
you can use:
set $terminal /usr/bin/urxvt
Also update documentation (manpage, userguide).
To make the code easier to read/write when checking if a client is
floating, introduce client_is_floating().
Details which are missing: A command to hide/show all floating clients,
moving/resizing clients with your mouse holding Mod1 (click anywhere
in the client, not just on its borders), resize/move by keyboard, select
next/previous client by keyboard
