tests: key of type integer

Signed-off-by: Jiri Kuncar <jiri.kuncar@gmail.com>
dictdiffer: support for int keys

* Improves `dot_lookup` function to support both dotted string lookup
  or list with keys.  (closes #12)

Signed-off-by: Jiri Kuncar <jiri.kuncar@gmail.com>
pep8: fix test for membership should be 'not in'

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
tests: py.test with doctests and coverage

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
git: ignore .cache directory

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>