robin_hood version 3.2.7

Important robin_hood.h stability fixes and improvements:

• fix include for old clang on darwin build
• no more static object required: got rid of the static dummybyte, reusing mMask when it's still empty.
• Per the standard, out-of-bounds pointer were undefined behavior. Now no out-of-bounds pointers are used any more.
• fixed a count() and .at() bug for empty maps
• fixed move of empty map
• Much more stringent compile warnings, with fixes: loads of cast warnings, __int128, fallthrough
• visual studio compile fix

Lots of infrastructure improvements:

• Complete rewrite of all unit tests
• switched from catch2 to doctest: much faster builds
• cmake all the things!