Serpent

- support for enum34 backport library for enums in older python versions.

1.25-dotnet
C code cleanup (code style, c 6 language level features)
Some small tweaks and attempt to fix an inconsistently running unit test

- LICENSE file included in release.

fix Python 3.7 deprecation warnings about importing ABC types from collections vs collections.abc

*python:*
- tighter limit on max recursion level to avoid RecursionError even better

*java:*
- **now requires Java 8 (JDK 1.8) minimum to compile & run!**
- Java 9 compatibility added.

- python 3.4's enum.Enum is now also accepted as immutable dict key or set element type.
- register_class is now preserving registration order so you can depend on correct and deterministic precedence.

Added checks in the serializer that prevents generating data that cannot be deserialized later.
The problem was that serpent allowed a non-hashable / non-immutable type as a dict key or set element.
This is now no longer allowed and an error is thrown if you try to serialize such a data structure.