adds keccak function manager

mythril/laser/ethereum/keccak.py

@@ -0,0 +1,17 @@
+from z3 import ExprRef
+
+class KeccakFunctionManager:
+    def __init__(self):
+        self.keccak_expression_mapping = {}
+
+    def is_keccak(self, expression) -> bool:
+        return str(expression) in self.keccak_expression_mapping.keys()
+
+    def get_argument(self, expression) -> ExprRef:
+        if not self.is_keccak(expression):
+            raise ValueError("Expression is not a recognized keccac result")
+        return self.keccak_expression_mapping[str(expression)][1]
+
+    def add_keccak(self, expression: ExprRef, argument: ExprRef):
+        index = str(expression)
+        self.keccak_expression_mapping[index] = (expression, argument)