Implement growing and shrinking pools

.. using 2 methods

Using 2 methods we know beforehand if the user wants to remove a prefix
from a pool, and incase he/she wants completion, *he can opt for not specifying a range.
Commit plajjan's gist

https://gist.github.com/plajjan/91c310603c4339e2879e
Whitespace: Add some empty lines above methods
Use global pool variable in resize methods
remove example code
Use correct variable in error message

Part of #146
Fix bug in helper-nipap

This makes helper-nipap a bit more tolerant to errors in that it will
find the first argument called 'nipap' and continue processing all
arguments after that first argument. This means that helper-nipap can be
called like "helper-nipap nipap address" or "helper-nipap address" and
it will still produce the same output.

Fixes #375.