Small modifications to DeriveUnit

Fixed init inconsitencies on DeriveUnit IO queues as well as function
naming. Updated test to stream output

test/manual/derive_unit.py

@@ -38,4 +38,13 @@ unit = DeriveUnit(uuid4(), process, [sig_a, sig_b], sig_r)
 val_a = ValueDescriptor(signal_id=sig_a.id, value=1, timestamp=0)
 val_b = ValueDescriptor(signal_id=sig_a.id, value=2, timestamp=10)
 
-print(unit.process_offline([val_a, val_b]))
+unit.put_data([val_a, val_b])
+
+try:
+    while True:
+        output = unit.get_output()
+        if output is not None:
+            print(output)
+
+except KeyboardInterrupt:
+    exit(0)