Bug-fix.

Changelog excerpt:
- Aggregating a single IP address with its own CIDR equivalent (i.e., a
  range containing just one IP address) produced output with a wider than
  expected range; Fixed.

v1.3.1

Slightly improved some PHPDoc annotations.

Fix typo in tests.

Removes broken tests.

Not sure how to fix these at the moment. Might reinstate them later if I
can figure it out.