Generator limit

[auerswal]

This pull request addresses GitHub issue #299 by:

• using the same maximum number of generated addresses for both range and CIDR arguments,
• fixing the off-by-one error in the generator limit, and
• increasing the limit to allow a 15-bit IPv4 prefix as generator input, or a range of the same size.

The generator limit is not exactly tested via CI, because pinging 100000 (or 100001) localhost IPv4 addresses takes more than 15 minutes on my computer. Testing 2^17-2 localhost IPv4 addresses takes more than 20 minutes on my computer. Thus I have tested this only manually.

[coveralls]

coverage: 85.622%. remained the same when pulling e6a607705fa2ac1f1e2ed40d36c120d8418dfe44 on auerswal:generator_limit into ab20b150b83af45a0f70fff2b40355f5878fd0d9 on schweikert:develop.