Updated hold create scenario to use Customer
Merge pull request #54 from remear/customer-scenarios

Updated hold create scenario to use Customer
Improvements to error handling

* Move factory for error classes into Error::createFromResponse (so Resource::convertError doesn't have to know about the internal structure of Error)

* Initialize Error::$codes only if necessary (the first time createFromResponse is called); don't initialize it just because the API is bootstrapped

* Improve Error::init: less code to do the same thing and remove hard-coded class name

* Error::createFromResponse returns an Error if it can't find a match (an improvement over returning an HTTPError)
Add card-declined => Declined error mapping
Scenario overhaul
Merge pull request #57 from remear/scenario-overhaul

Scenario overhaul
Update test suite to check for \Balanced\Errors\Error instead of \RESTful\Exceptions\HTTPError
Merge pull request #56 from jbafford/feature/error-handling

Improvements to error handling
Scenario updates