Added find_as_hashes functionality for ActiveResource

Changes to the README:

# ActiveResource

The equivalent methods are available in ActiveResource as well, providing
similar benefits.

## Methods

The hashes that return are essentially the xml or json data hashified.

* `all_as_hashes` works similarly to `all`, but returns the results as
  an array of hashes.
* `find_as_hashes` works similarly to `find`, but returns the results as
  an array of hashes.
* `first_as_hash` works similarly to `first`, but returns a hash of the
  first matching record.
* `last_as_hash` works similarly to `last`, but returns a hash of the
  last matching record.

## Usage

To enable the use of these methods, simply add this line to the top of your
ActiveResource class.

`require 'active_resource/find_as_hashes'`

## Examples

    > User.all_as_hashes(:active => 1)
    => [
      {:id => 123, :name => "Joe User", :active => 1,},
      {:id => 456, :name => "Jane User", :active => 1}
    ]

    > User.first_as_hash(:active => 1)
    => {:id => 123, :name => "Joe User", :active => 1}