merged w/ latest develop

b_asic/core_operations.py

b_asic/graph_component.py

b_asic/operation.py

b_asic/port.py

b_asic/signal.py

b_asic/signal_flow_graph.py

b_asic/simulation.py

b_asic/special_operations.py

test/conftest.py

test/fixtures/operation_tree.py

test/fixtures/port.py

test/fixtures/signal.py

test/fixtures/signal_flow_graph.py

test/test_abstract_operation.py

test/test_core_operations.py

test/test_graph_id_generator.py

test/test_inputport.py

test/test_operation.py

test/test_outputport.py

test/test_print_sfg.py