Merge pull request #1 from rurban/master

no %%llu on uint64_t, #include <limits> for std::numeric_limits -- will be fixed for PRIu64
Turned %lu and %llu formats for uint64_t into PRIu64.
Removed the references to DELETED_BUCKET.

The code for the Robin Hood hashing with backward shift deletion
was started as a copy and paste from the Robin Hood hashing with
tombstones. References to DELETED_BUCKET had remained and were
confusing for newcomers to the code and needed to be cleaned up.