Make is_nested more robust and fix capitalization issue.

Also, add a test for the is_nested method and all its branches.
Fix bad function name in exception message
Avoid division by 0 in normalize and remove duplicate normalize code
Move dimensions definition so it is created immediately before reference

This fixes https://github.com/cbmi/avocado/issues/102 where it was
possible to construct a case where d was 1 and dimensions was still
referenced.
Support 1-dimensional points in weighted_count method
Add more tests to increase code coverage for kmeans package

The kmeans package is covered except for a single branch in the
`weighted_counts` method. I've had some difficulty reaching that branch
because the distances returned from `kmeans_optm` are never quite 0
because of the floating point precision involved in that method
resulting in near 0 distances in all my test cases.
Merge pull request #103 from cbmi/kmeans-expanded-tests

Expanded tests for kmeans package