xxHash v0.7.1

The main feature of this release is an update of XXH3, building upon many user feedbacks during this test period. The main points are :

• Secret first : the algorithm computation can be altered by providing a "secret", which is any blob of bytes, of size >= XXH3_SECRET_SIZE_MIN.
• seed is still available, and acts as a secret generator
• As a consequence of these changes, note that new return values of XXH3 are not compatible with v0.7.0
• updated ARM NEON variant by @easyaspi314
• Streaming implementation is available
• Improve compatibility and performance with Visual Studio, with help from @aras-p
• Better integration when using XXH_INLINE_ALL : do not pollute host namespace, use its own macros, such as XXH_ASSERT(), XXH_ALIGN, etc.
• 128-bits variant provide helper function, for comparison of hashes.

Note that XXH3 is still considered experimental at this stage. It will have to remain stable for at least 2 releases before being branded "stable". After which stage, the algorithm and produced results will no longer evolve.

Several general improvements are also present in this release :

• Better clang generation of rotl instruction, thanks to @easyaspi314
• XXH_REROLL build macro, to reduce binary size, by @easyaspi314
• Improved cmake script, by @Mezozoysky
• Full benchmark program provided in /tests/bench