Add Customer#default_tax_code_ref
Merge pull request #119 from copyhacker/add_customer_default_tax_code_ref

Add Customer#default_tax_code_ref
Added a note about using Marshal for objects in Session
Merge pull request #121 from mgates/rails-4.1-readme-fix

Added a note about using Marshal for objects in Session
Add CurrencyRef to Customer
Add CurrencyRef to Customer reference_setters
Merge pull request #122 from harvesthq/add-currency-to-customer

Add CurrencyRef to Customer