Correctly handle integers in ipaddr filter

If integers are passed to 'ipaddr' filter, they will now be interpreted
as IPv4 or IPv6 addresses. Special format 'integer/prefix' will be also
interpreted and converted to IPv4/IPv6 CIDR format.
Merge pull request #28 from drybjed/ipaddr-numbers

Correctly handle integers in ipaddr filter
Add 'ipwrap' filter

'ipwrap' is a special version of 'ipaddr' filter, which adds brackets to
IPv6 addresses and lets everything else through without changes.
Merge pull request #29 from drybjed/ipwrap

Add 'ipwrap' filter