raise explicit error when shopify call limit header is unavailable
removing code that's been backported from ActiveResource
remove re-definition of headers method in ShopifyAPI::Base
update backported version of ActiveRecord::Base.build
include root in json for recent versions of ActiveResource
apply User-Agent string dynamically rather than statically
remove code from old versions of activeresource
use a centralized headers hash
adding basic gemfile
Merge branch 'add_gemfile' into activeresource_4_0_0
Use correct http header name for checking API limits.
Merge activeresource_4_0_0 into master