Blender Git Loki

Initial GHash-enhancements experiments.

This commit adds:
*Some Murmur-based hasing helpers for GHash;
*A (very basic) switch between key-to-bucketidx using modulo or binary-AND;
*Some gtests to make some comparisons.

First test results seem to show that:
* murmur is much much quicker for string keys, with approximately same hash quality;
* org ghash is much much quicker for int keys, but with much worse hash quality than murmur-based one;
* key-to-bucketidx method does not seem to make much difference so far.

Nothing definitive here yet, obviously.