Adding Ascon, an AEAD lightweight cipher.

[armfazh]

Reference: https://ascon.iaik.tugraz.at/index.html

Benchmarks:
old= naive substitution layer
new= 64-bit operations (constant-time)

benchmark	Operation	old MB/s	new MB/s	speedup
Ascon128	Open-64-8	1.71	125.59	73.44x
Ascon128	Seal-64-8	1.58	123.48	78.15x
Ascon128	Open-1350-8	2.86	211.97	74.12x
Ascon128	Seal-1350-8	2.72	210.11	77.25x
Ascon128	Open-8192-8	3.06	203.36	66.46x
Ascon128	Seal-8192-8	2.91	209.82	72.10x
Ascon128a	Open-64-8	2.19	157.34	71.84x
Ascon128a	Seal-64-8	2.09	155.94	74.61x
Ascon128a	Open-1350-8	3.94	309.84	78.64x
Ascon128a	Seal-1350-8	4.15	290.40	69.98x
Ascon128a	Open-8192-8	4.14	308.30	74.47x
Ascon128a	Seal-8192-8	4.17	301.98	72.42x

[bwesterb]

Nice moving to int64. How does the performance improve? The substitution table still isn't constant time.