ZstdNet 1.4.5

Main changes:

• libzstd v1.4.5
• Span support (#19)
• Streaming support (#18)
• Advanced parameters APIs support

Some other changes:

• libzstd.dll now cross-compiled using (i686|x86_64)-w64-mingw32-gcc -DZSTD_MULTITHREAD -DZSTD_LEGACY_SUPPORT=0 -pthread -s instead of msvc for performance reasons
• ZstdException error codes exposed
• On buffers close to 2GB Wrap now tries its best, but if source is uncompressible and the size is too large, ZstdException with ZSTD_error_dstSize_tooSmall will be thrown (#21)
• Buffer pooling on Wrap without dst param

Possibly breaking changes:

• Decompressor.GetDecompressedSize() now throws ZstdException instead of returning 0 on error
• ZstdException with error code ZSTD_error_dstSize_tooSmall instead of InsufficientMemoryException on Wrap if destination buffer too small
• ZstdException with error code ZSTD_error_dstSize_tooSmall instead of ArgumentOutOfRangeException on Unwrap if destination buffer too small