Remove draw_queue_t type

There's only one draw queue, why export it and leave it to target.c to create
it? Now the global draw queue is internal to draw_queue.c and doesn't need to
be passed to draw as an argument.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Add stdlib.h to quat.h

We were only getting by without it by chance.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Introduce draw_op API

This subsumes the loose functionality in draw_queue.c, which goes away. Draw
ops are a sort of shell over states, which say what to do while in the state as
well. This should eventually capture some of the ancillary stuff from states
themselves. We might also be able to sink states into the interior and use
these instead.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>