Update tests to reflect passing subsection parts

Update the tests for lookup_by_ilcs() to try to lookup elements
by subsection bits.

Also change the signature of lookup_by_ilcs to allow [arbitrary
argument
lists](https://docs.python.org/2/tutorial/controlflow.html#arbitrary-argument-lists) to be able to pass in the subsection parts of the ILCS reference.

These tests won't pass but are there as an example for @bepetersn
to continue this work.

Addresses https://github.com/sc3/python-iucr/issues/3
added failing tests for lookup_by_ilcs using the bits interface
add better tests for lookup by ilcs bits
improve subsection bit lookup test; implement backing off by subsections
remove unnecessary lib
Merge pull request #6 from bepetersn/handle_subsections

Fixes #3; allow passing subsections to lookup_by_ilcs()
Merge pull request #9 from sc3/handle_subsections

Handle subsections