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/AstroBWT.h

@@ -33,9 +33,14 @@
 struct cryptonight_ctx;
 
 
-namespace xmrig { namespace astrobwt {
+namespace xmrig {
 
-bool astrobwt_dero(const void* input_data, uint32_t input_size, void* scratchpad, uint8_t* output_hash, int stage2_max_size);
+class Job;
+
+namespace astrobwt {
+
+bool init(const Job&);
+bool astrobwt_dero(const void* input_data, uint32_t input_size, void* scratchpad, uint8_t* output_hash, int stage2_max_size, bool avx2);
 
 template<Algorithm::Id ALGO>
 void single_hash(const uint8_t* input, size_t size, uint8_t* output, cryptonight_ctx** ctx, uint64_t);
@@ -44,4 +49,4 @@ template<>
 void single_hash<Algorithm::ASTROBWT_DERO>(const uint8_t* input, size_t size, uint8_t* output, cryptonight_ctx** ctx, uint64_t);
 
 
-}} // namespace xmrig::argon2
+}} // namespace xmrig::astrobwt