Data depenencies printer: add example and improve output

examples/printers/data_dependencies.sol

@@ -0,0 +1,15 @@
+contract MyContract{
+    uint a = 0;
+    uint b = 0;
+    uint c = 0;
+
+    function setA(uint input_a, uint input_b) public{
+        setB(input_b);
+        a = input_a;
+    }
+
+    function setB(uint input) internal{
+        b = input;
+    }
+
+}

slither/printers/summary/data_depenency.py

@@ -8,8 +8,8 @@ from slither.analyses.data_dependency.data_dependency import get_dependencies
 from slither.slithir.variables import TemporaryVariable, ReferenceVariable
 
 def _get(v, c):
-    return [d.name for d in get_dependencies(v, c) if not isinstance(d, (TemporaryVariable,
-                                                                        ReferenceVariable))]
+    return list(set([d.name for d in get_dependencies(v, c) if not isinstance(d, (TemporaryVariable,
+                                                                               ReferenceVariable))]))
 
 class DataDependency(AbstractPrinter):