AVX2 optimized code for AstroBWT

Added "astrobwt-avx2" parameter in config.json, it's turned off ("false") by default.

4-5% speedup on CPUs with proper AVX2 support (AMD Ryzen starting with Zen2, Intel Core starting with Haswell).

There will be no speedup on the following CPUs:

- Intel Pentium/Celeron don't support AVX2
- AMD Zen/Zen+ have only half-speed AVX

GCC compiled version is faster without AVX2, MSVC compiled version is faster with AVX2

src/crypto/astrobwt/sha3_256_avx2.S

@@ -0,0 +1,50 @@
+;# XMRig
+;# Copyright 2010      Jeff Garzik              <jgarzik@pobox.com>
+;# Copyright 2012-2014 pooler                   <pooler@litecoinpool.org>
+;# Copyright 2014      Lucas Jones              <https://github.com/lucasjones>
+;# Copyright 2014-2016 Wolf9466                 <https://github.com/OhGodAPet>
+;# Copyright 2016      Jay D Dee                <jayddee246@gmail.com>
+;# Copyright 2017-2019 XMR-Stak                 <https://github.com/fireice-uk>, <https://github.com/psychocrypt>
+;# Copyright 2018      Lee Clagett              <https://github.com/vtnerd>
+;# Copyright 2018-2019 tevador                  <tevador@gmail.com>
+;# Copyright 2000      Transmeta Corporation    <https://github.com/intel/msr-tools>
+;# Copyright 2004-2008 H. Peter Anvin           <https://github.com/intel/msr-tools>
+;# Copyright 2018-2020 SChernykh                <https://github.com/SChernykh>
+;# Copyright 2016-2020 XMRig                    <https://github.com/xmrig>, <support@xmrig.com>
+;#
+;#   This program is free software: you can redistribute it and/or modify
+;#   it under the terms of the GNU General Public License as published by
+;#   the Free Software Foundation, either version 3 of the License, or
+;#   (at your option) any later version.
+;#
+;#   This program is distributed in the hope that it will be useful,
+;#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+;#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;#   GNU General Public License for more details.
+;#
+;#   You should have received a copy of the GNU General Public License
+;#   along with this program. If not, see <http://www.gnu.org/licenses/>.
+;#
+
+.intel_syntax noprefix
+#if defined(__APPLE__)
+.text
+#define DECL(x) _##x
+#else
+.section .text
+#define DECL(x) x
+#endif
+
+#define ALIGN .balign
+#define dq .quad
+
+.global DECL(SHA3_256_AVX2_ASM)
+
+#include "sha3_256_avx2.inc"
+
+KeccakF1600_AVX2_ASM:
+	lea r8,[rip+rot_left+96]
+	lea r9,[rip+rot_right+96]
+	lea r10,[rip+rndc]
+
+#include "sha3_256_keccakf1600_avx2.inc"