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

cmake/astrobwt.cmake

@@ -23,6 +23,16 @@ if (WITH_ASTROBWT)
             src/crypto/astrobwt/salsa20_ref/salsa20.c
         )
     else()
+        if (CMAKE_SIZEOF_VOID_P EQUAL 8)
+            enable_language(ASM_MASM)
+            add_definitions(/DASTROBWT_AVX2)
+            if (CMAKE_C_COMPILER_ID MATCHES MSVC)
+                list(APPEND SOURCES_CRYPTO src/crypto/astrobwt/sha3_256_avx2.asm)
+            else()
+                list(APPEND SOURCES_CRYPTO src/crypto/astrobwt/sha3_256_avx2.S)
+            endif()
+        endif()
+
         list(APPEND HEADERS_CRYPTO
             src/crypto/astrobwt/Salsa20.hpp
         )