Add more WDF adaptors

b_asic/__init__.py

b_asic/core_operations.py

b_asic/sfg_generators.py

b_asic/wdf_operations.py

docs_sphinx/api/wdf_operations.rst

examples/lwdfallpass.py

examples/thirdorderblwdf.py

test/test_core_operations.py

test/test_sfg.py

test/test_sfg_generators.py

test/test_wdf_operations.py