waynerobinson/xeroizer — pull request #178 by rjocoleman (2014-11-28 23:19:22+00:00)
Title: add GET ContactGroups

First contribution - sorry if I've not followed your preferred methodology.

This is a simple PR to add support for reading the `ContractGroup` model.

As per the Xero docs it will output all contacts on a GET for a specific group: http://developer.xero.com/documentation/api/contactgroups/#title9

e.g:

```ruby
@client.ContactGroup.all
# => [#,
#]

@client.ContactGroup.find('97bbd0e6-ab4d-4117-9304-d90dd4779199')
# => #, #, #]>
```