Support inet/cidr operators

[LordMike]

As pr. Gitter chat.

For a project, I need to be able to perform containment/comparison operations on inet/cidr types, so the operators in the below documentation would be awesome to have :).

https://www.postgresql.org/docs/9.3/static/functions-net.html

[roji]

@LordMike can you please provide some more detail on exactly which operators you need in your application?

[LordMike]

For this specific project, contains-or-equals operators. So: <<, <<=, >> and >>=.

[austindrenski]

It looks like this could be implemented in the same way as #323 (extension stubs + attributes).

@roji If no one is actively working on this, I'm happy to volunteer to take this one.

[roji]

@austindrenski you're welcome to work on this, it should be even easier than ranges (no generics). However, please take into account my comment on the design before starting to implement, so we're agreed on how we want translators to look like.

[austindrenski]

This feature was completed in #407 and #535.