removed unnecessary copying of exception
added factory class stub (#34)
added Symfony DI container as dependency (#34)
added container factory stub (#34)
added test case stub (#34)
added comments (#34)
implemented some tests (#34)
introduced helper methods and test data (#34)
implemented some tests (#34)
fixed file path (#34)
implemented container factory (#34)
fixed type hint (#34)
added configuration class stub (#34)
fixed typo
implemented tests (#34)
implemented configuration (#34)
created test case for adapter factory that uses a container (#34)
implemented adapter factory that uses a container (#34)
added possibility to explicitly configure a backend adapter class, which
- allows usage of an external, non-Erfurt adapter
- avoids coupling keys in the ini files to class names
  - allows using the same adapter in different configurations
(#34)
configuration now uses temp directory if no cache directory is provided (#34)