xxHash v0.5.0

• Semantic versioning
  • availability of XXH_versionNumber() and XXH_VERSION_NUMBER for user-side test
• New canonical API, suggested by @t-mat
• New : Private API mode
• New : command line option --little-endian to display hashes with said convention
• Updated cmake install, thanks to @romange
• Breaking API change for streaming version using static allocation :
  • XXHnn_state_t is now incomplete type, and cannot be allocated directly on stack
    • required for better conformance with strict-aliasing rules
  • use XXHnn_CREATESTATE_STATIC() instead (see xxhash.h for details)