setup: rename `CONTRIBUTING` to `CONTRIBUTING.rst`

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
test: no empty instructions

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
dictdiffer: fix for empty list instructions

* Addresses an issue when `reversed` iterator was evaluated as `True`
  causing empty instruction set to appear.  (closes #30)

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