Able to specify keys on the attributes method

What do you guys think about this?

Instead of doing this:
```ruby
attribute :a_foo => :a_bar 
attribute :b_foo => :b_bar 
attribute :c_foo => :c_bar 
```

do this:
```ruby
attributes :a_foo => :a_bar, :b_foo => :b_bar, :c_foo => :c_bar 
```

I don't know if anyone has proposed this, if so feel free to close this :smiley: