Port TinyAES-128 to be thread safe.

This is a bit of a proof of concept port to hack tiny-AES128-C into something that can run thread safe.
This is just done by moving the global static state variables to a struct and allocating that on the stack instead.

I know that tiny-AES128-C was engineered in the way it was to run nice on small devices, but for our use case, embedding it into a library thread safety would be key.