Add Metafields mixin to the Customer resource.

The ability to add metafields to Customers was recently added in Shopify.
Fixed double root bug with ActiveSupport 3.2.0
Fixed tabbing
Fixed failing tests on ruby 1.8.7
Merge pull request #16 from dennisoconnor/ActiveSupport-3.2.0

Fixed double root bug with ActiveSupport 3.2.0
Packaging for 2.3.0 release.
Added cart resource to the api
Automatically add missing .myshopify.com to domain for shopify add.

Allows for a shorter alias for the connection name without having to
specify the full domain.

Closes #15.
Include library versions in user-agent header.
Backport ActiveResource patch to inherit headers from parent classes.

See rails commit c5bf53822f5887c9b235ceef388b1c8a977bcc88.
Merge branch 'user-agent'
work with oauth2
remove unused methods, update tests.
Put token in Header and change activation method
Make sure headers are properly cleared and set.
Update tests

Add tests
Add back validates signature
Merge pull request #19 from redronin/oauth

replaces the legacy auth code with Oauth2 functionality
Bumps the version number for the Oauth2 release
Updates the read me for OAuth 2.0