Add ability to pass configuration options via a service ctor.
Change parent class of service classes.

Service classes will no longer have BaseService as their parent. These
classes will need to extend a class designed for the eBay service. E.g
TradingBaseService. These new parent classes will contain information
relating to the service, E.g. class constants.
Fix namespace of parent service classe.
Fix service test so that it tests for correct base class.
Simplify tests.
Merge branch 'tests' into develop
Generate PHP code for eBay enums in Enum directory.

PHP code eBay enums are no longer generated in the same directory as
regular eBay types.
Merge branch 'enums' into develop
Service class is passed HttpClient instance via ctor.
Merge branch 'http-client' into develop
Return response when sending API request.
Merge branch 'service' into develop
Pass response class name when calling operation.
Merge branch 'call-operation' into develop
Remove version number of api urls.

Now just download latest WSDL instead of a specified version.
Merge branch 'remove-api-version' into develop
Update code so that it can be included in releases.
Merge branch 'release' into develop