Add WIP feature for posting many invoices at once; add WIP spec to implement first part of that...
Implement the serialisation side of posting several invoices
Naive implementation of the deserialise side of posting many invoices
Generate URLs with ?SummarizeErrors=false when appropriate
Happy path deserialising now only uses deserialise_from_node

This should pave the way for better error handling
Refactor APIResponse and change APIException so API exception processing works similarly to successful processing
remove WIP status from the first posting-several-invoices scenario
Add WIP feature for posting some valid and some invalid invoices
APIResponse mechanism copes with some successful and some unsuccessful objects in a response

* post-some-valid-and-some-invalid feature no longer WIP :-)
Point the VCR cassette directory for specs to the correct place
Add simple Addresses object
Fill out Addresses object, move EmptyAddresses into addresses.rb
Add Address object
Move EmptyAddress into address.rb
Add trivial Contact serialiser; updated XML Schemas repo to validate these
Filled out Objects::Addresses & Objects::Address to support filling out the Contact serialiser