Remember to increment number of items in target_draw

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Add target steps, remove sequential dependencies

We introduce a new step type for targets which executes another target. In
practice this is essentially equivalent to sequential dependencies, so we can
now remove those.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Add Clear steps for targets

We now can use target steps to clear buffers, which totally obsoletes the
generic target buffer-clearing mechanism (now removed).

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

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

We can now do everything with the sequentialized "steps" system, and the state
array.

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