Insecure malloc and memcpy functions used

[patrickdunsheecubic]

In a recent audit, testers flagged use of insecure function memcpy and malloc. We were recommended to use memcpy_s and calloc as alternatives, and wanted to pass that recommendation to you all to improve security of the library.

Thank you for your consideration!

[PetteriAimonen]

Might make sense having it as a compilation option, but memcpy_s is only supported in C11 and I intent to retain C89 support.

Nanopb does not currently use malloc() at all, only realloc().