Added prototypes to fix warnings.
Ignore new generated files.
Using the nettle_dsa_params_init as 3.0 indicator appears safer to me than a compat header file.
Don't use our own PRNG. Some cleanup.
Fixed comment.
Remove the backtrace mechanism in Alert.
Turn seq_num into an integer.
Build: Use the recommended way to detect Nettle API differences.

The main Nettle developers recommend using the function renaming
macros to detect Nettle API differences.

In this case we use <nettle/dsa.h>'s remapping of dsa_params_init
to nettle_dsa_params_init to detect Nettle 3.0 or later.
Nettle: Fixed typo in macro name.
Nettle.CHACHA_POLY1305: Initial implementation.

Implements the CHACHA-POLY1305 AEAD cipher algorithm, and
maps it to Crypto.ChaCha20.POLY1305.