Typedpy

Following issues:
Issue 25 - serialization of inherited Structures
Issue 26 - serialization of Map
Issue 27 - minor improvement - inspect type hints of a function - if it is Field, the function can be used as a Field in a Structure class definition.
Issue 28 - DateTime Field
Issue 29 - Immutable can be changed through a reference
Issue 30 - non typedpy attributes do not serialize correctly

23

18
19
20
21

Issues:
15
16
17

Support Python 3.8. Dropped support for Python 3.5.

- Tuple[String] defines a tuple of any number of strings
- Added support for python 3.7
- Removed python 3.4 support
- Added DecimalNumber type, which accepts decimals
- Issue 13 - assessor works when field was not set
- Support for default values for fields