A simple function that tells you whether a link DOM node is 'external'.
A link is external if it:
- has the attribute rel="external"
- has the attribute target and the value is not _self
- is an absolute link
- is a telephone link
- is a mailto link
var external = require('external-link');
var link = document.querySelector('a');
external(link);
2.0.0 - changed handling of target so that any value other than _self will make it external