Draft of attribute syntax API

This RFC probably isn't the place for it, but there was recently an issue filed that points out you cannot provide an absolute attribute path in the field with anchors. https://github.com/opscode/chef/issues/1855

Given:
```
node[:apache2][:magic][:fqdn] = "www.example.org"
node[:fqdn] = "tom.example.org"
```

Both `knife node search fqdn:www.example.org` and `knife node search fqdn:tom.example.org` would return this node.

So, what would this return? `search(:node, "fqdn:www.example.org")`