Resolve "Operation Replacement in a SFG"

Added method with tests for replacing multiple operations in a sfg with another operation with the same amount of input / output ports. Closes #17

test/test_core_operations.py

@@ -4,7 +4,7 @@ B-ASIC test suite for the core operations.
 
 from b_asic import \
     Constant, Addition, Subtraction, Multiplication, ConstantMultiplication, Division, \
-    SquareRoot, ComplexConjugate, Max, Min, Absolute, Butterfly, MAD
+    SquareRoot, ComplexConjugate, Max, Min, Absolute, Butterfly
 
 class TestConstant:
     def test_constant_positive(self):
@@ -162,9 +162,4 @@ class TestButterfly:
     def test_buttefly_complex(self):
         test_operation = Butterfly()
         assert test_operation.evaluate_output(0, [2+1j, 3-2j]) == 5-1j
-        assert test_operation.evaluate_output(1, [2+1j, 3-2j]) == -1+3j
+        assert test_operation.evaluate_output(1, [2+1j, 3-2j]) == -1+3j
 
\ No newline at end of file
-    def test_split(self):
-        but1 = Butterfly()
-        split = but1.split()
-        assert len(split) == 2