Refactoring: dispatch "core" package modules into structs and utils, as it does not have a lot of sense anymore.

tests/structs/test_inputs.py

@@ -19,8 +19,8 @@ from queue import Empty
 import pytest
 
 from bonobo.constants import BEGIN, END
-from bonobo.core.inputs import Input
 from bonobo.errors import InactiveWritableError, InactiveReadableError
+from bonobo.structs.inputs import Input
 
 
 def test_input_runlevels():

tests/util/test_statistics.py

@@ -1,4 +1,4 @@
-from bonobo.core.statistics import WithStatistics
+from bonobo.util.statistics import WithStatistics
 
 
 class MyThingWithStats(WithStatistics):