API documents are essential

[CarpenterLee]

Thanks for the SlabHash implementation.
When I am trying to use gpu_hash_table, there are no API docs in the source code, which really confuses me. So would you mind to add essential documents of the main API, especially for class gpu_hash_table and GpuSlabHash.
I am confused by buildBulk() and buildBulkWithUniqueKeys(), searchIndividual() and searchBulk().