This also removes the old poly1305_auth interface, as it no longer serves any
function. The new Poly1305 class based interface is more modern and safe.
This code is taken from poly1305-donna-32.h, poly1305-donna.h, poly1305-donna.c
from https://github.com/floodyberry/poly1305-donna, commit
e6ad6e091d30d7f4ec2d4f978be1fcfcbce72781, with the following modifications:
* Coding style (braces around one-line indented if/for loops).
* Rename unsigned long (long) to uint32_t and uint64_t.
* Rename poly1305_block_size to POLY1305_BLOCK_SIZE.
* Adding noexcept to functions.
* Merging poly1305_state_internal_t and poly1305_context types.
* Merging code from multiple files.
* Place all imported code in the poly1305_donna namespace.
