Fix snappy roundtrip failures on big-endian 64-bit architectures

Bug: https://github.com/Sereal/Sereal/issues/47
Bug-Debian: https://bugs.debian.org/742409

csnappy_compress_fragment() was returning nonsense because
GetUint32AtOffset() would always take the little endian code path.
Release v3.002_001 - Fix 64 bit Big-Endian and other minor changes