This commit introduces:
    - the infrastructure for optimizer hints;
    - hints for join buffering: BNL(), NO_BNL(), BKA(), NO_BKA();
    - NO_ICP() hint for disabling index condition pushdown;
    - MRR(), MO_MRR() hint for multi-range reads control;
    - NO_RANGE_OPTIMIZATION() for disabling range optimization;
    - QB_NAME() for assigning names for query blocks.