Draft of attribute syntax API

I think the escaping support is important, at least for me.

Some attribute examples using dots in keys:

```ruby
node['network']['interfaces']['eth0']['addresses']['11.22.33.44']['netmask'] # set by ohai
node['proftpd']['virtual_host']['ftp.example.com']['default_root']
node['myapp']['conf']['settings.yml']['dbname']
```