Fix log message format
Remove SerializationContext.registerProtoFiles(String... classpathResource)

This was only used by tests and can be easily replaced by registerProtoFiles(FileDescriptorSource source).
Provide documentation annotations for message, field and enum descriptors

Parse java-like annotations from the doc comment and provide the syntax tree to the user via GenericDescriptor.getAnnotations() and FieldDescriptor.getAnnotations().