Signature scanner engine

There are 2 essential engine implementations (pre compiled and SIMD) which are repesented in code as:

• SignatureScannerAvxEngine
• SignatureScannerSseEngine
• SignatureScannerCompiledEngine

The first two (Avx and SSE) use respectively AVX256 instructions and if they're not available fallbacks to SSE (the latest available version). Formulas: SimdVectorRegisterLength = maximum vector length in bytes -> for avx2: 256/4 = 32 -> for sse: 128/4 = 16