Add new compilation flag (AESNI_EMU) to enable AESNI emulation.
This flag is disabled by default, so the AESNI emulation code
is not compiled unless the flag is set.

ZUC does not use any constant time lookup functions,
so it should not be in the list of algorithms depending on
these functions in README.

- Added AES-ECB to man page recommendations
- Minor fix in README recommendations table

Now that there is an SSE and an AVX implementation,
there is no need to have an scalar implementation for Chacha20.

Initial Chacha20 AVX512 implementation done using XMM registers
only, handling only 64 bytes at a time.