LeasePool: fix parameter list of 3 methods.

new_lease_any, new_lease and remove should override the respective
superclass methods, but since they declare slightly different formal
parameters, they are compiled as overloads rather than overrides.
LeasePool: standardize indentation to 4 spaces.
LeasePool: fix usage example.
LeasePool: include END address in the pool.

I think it's more intuitive this way.
Merge pull request #3 from Pesa/master

DHCPLeasePool: several improvements.