Adding linode.ip.swap and linode.ip.addpublic

## Summary

Due to a project I'm working on, I needed to call the API method to swap IP addresses between Linodes. Let me know if anything else is needed to get this merged. Thanks!

## Approach

Add the required API method and increment the minor version number.

## Risk Factor

Low. I have tested it locally.
If I'm reading the spec correctly, this should also return IPAddress, the IP address that was added