added support for extended email formats
added some useful type checks to the various extract methods
added a convenience function to Structure
a small bug fix
incrementing version tag
a small bug fix
added support for ignore_null flag on fields
provide autogeneration of polymorphic_on field
fixed some gaps with default generation for polymorphic structures
added initial interpolation implementation
implemented polymorphic element instantiation
StructuredText format should handle None/null
fields should properly describe parameters which contain field classes
better approach to reconstructing fields
added support for proper recursive interpolation