added support for slices

[nat3Github]

before merging a quick warning:

• i removed a lot of code, specifically error handling, fastDeserialization and deserializeIntoPointer
• i removed code i did not understand what its doing!
• i have not measured performance regressions!
• i broke the api! (deserialize now always takes an allocator and if its not used someone can pass undefined as allocator)
• i did not check if custom ser/de fns works (cause i dont use that)

that being said. All tests pass and i've added another one that has slices.

im always happy about feedback.
greetings!