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_sfg.py

 import pytest
 
-from b_asic import SFG, Signal, Input, Output, Constant, Addition, Multiplication
+from b_asic import SFG, Signal, Input, Output, Constant, Addition, Multiplication, MAD
 
 
 class TestInit:
@@ -254,3 +254,22 @@ class TestReplaceComponents:
             assert True
         else:
             assert False
+
+class TestReplaceOperations:
+    def test_replace_mul_add_with_MAD(self):
+        in1 = Input()
+        in2 = Input()
+        in3 = Input()
+        mul1 = in1 * in2
+        add1 = mul1 + in3
+        out1 = Output(add1)
+
+        sfg = SFG(inputs=[in1, in2, in3], outputs=[out1])
+        assert len(sfg.operations) == 6
+
+        mad1 = MAD()
+
+        sfg.replace_operations([in1, in2, in3], [out1], mad1)
+        assert len(sfg.operations) == 5
+        assert {add1, mul1} not in sfg.operations
+        
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