Adds Avalara calculator
Updates avalara calculator to use generate invoice before computing
Refactors calculator
Adds avalara dependency
Adds SpreeLocalTax::Avalara and spec
Adds invoice generator
Adds logic to add lines
Refactor invoice generator to invoice builder
Adds InvoiceBuilder#add_destination
Refactors SpreeLocalTax::Avalara module
Adds SpreeLocalTax::Avalara#compute
Adds configuration options for avalara
Adds logic & specs to ensure avalara username/password is set
Adds logic to use either shipping or billing address
Adds logic to configure and set origin address
Updates response handling to iterate thru lines
Adds invoice builder spec
Removes first/last name from destination address
Adds destination address to builder
Adds origin address to builder