Improve structure

[jdreesen]

In preparation of a v1.0 release, I'd like to propose a different structure for the code.

The primary interfaces (Converter, Populator and TargetFactory) are now in the top-level namespace (this is to prevent namespaces like ...\Converter\Converter), while their implementations, etc. stay in a folder named after the interface. Some related things also moved into those folders (e.g. the ConverterSelector interface) and some classes were renamed.

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Here's what I did:

• Moved Converter interface to the top-level namespace
• Moved Populator interface to the top-level namespace
• Moved TargetTypeFactory interface to the top-level namespace and renamed it to TargetFactory
• Renamed DefaultConverter to GenericConverter
• Renamed DefaultConverterContext to GenericContext and moved it to the Converter\Context namespace
• Renamed ConverterStrategyHandler to StrategicConverter
• Moved ConverterSelector to the Converter\Strategy namespace
• Renamed ConverterPopulator to ConvertingPopulator
• Renamed MappedPropertyPopulator to PropertyMappingPopulator

Note I didn't touch the CacheManagement namespance and the CachedConverter class, because they'll get deleted with #36.