- cleanups
- add sparse iter instructions
- merge "root" and "sparse iter" programs together
- move program execution to new file program_runtime.h
- simplify EOD execution
This changes all the execute_graph() interfaces so that instead of
mutating a std::set of vertices, they accept an initial flat_set of
states and return a resultant flat_set of states after execution.
(Note that internally execute_graph() still uses bitsets)
This is both faster and more flexible.
