actually added own header to c file
renamed add function to op_add for consistency
changed expr_s from GSList nums to bit field

bit field now keeps track of valid nums by lookup in an array
expr copy and free functions don't need to free it
expr_new has no arguments, call in manager changed
added push_num, plus unfinished tests in manager

added push_num routine
unfinished scaffolding in manager, doesn't print result
updated makefile dependencies
added some comment notes