Start mouse support.

It is possible to move a window with MODKEY+Button1, but the clients are
not yet restacked, and floating is not yet implemented.

... overall it's got a little glitchy feeling (even though everything
works fine - it's just that "everything" is not much).
Forgot to add mouse config.
Integrate reltox() into movews().
Add floating windows.

Upon moving a window, its 'floating' state get enabled and the window
gets raised.

Start adding resize feature (not yet finished).
Respect size hints to properly handle terminal windows.

The resizing is yet a bit buggy at the beginning, as the mouse jumps
around (XWarpPointer() does not seem to have an effect there).

Minimal size is not yet checked, so keep it sane while playing around
with the resize.
Update README and config.h.
Merge branch 'mouse'.

Enables mouse support for moving clients and resizing them.