Add ability to extend associations with Resource.decorate.

Signed-off-by: Dane Jensen <dane@rightscale.com>
It's most definitely not the same in the resulting output that gets evaled:
```ruby
puts 'key'.to_s    # => key
puts 'key'.inspect # => "key"
puts :key.to_s     # => key
puts :key.inspect  # => :key
```