Implement bitwise-or operation.

This is useful for calculating the broadcast address.  For example:

    var broadcast = ip.or(ip.not(netmask), address);

Broadcast addresses are not used in ipv6, but this provides the basic
bitwise-or for both protocols.

Tests for ipv4, ipv6, and mixed case included.
Merge pull request #5 from wanderview/bitwise-or

Implement bitwise-or operation.