Tread-safety for Libs

[embetrix]

all the libraries built from this project have no thread-safety guarantees and are unsafe to use from multiple threads concurrently (exeption for piolib)

Depending on intended usage, options include:

• add mutex serialization to each library (following piolib's pattern)

• Replacing static return buffers with caller-provided buffers or thread-local storage

• or document the libraries as single-threaded only

[timg236]

I think this is a NGTF, there's no reason to explicitly assume thread safety