Row sparse disk

[marekkokot]

Implementation of row_sparse_disk and row_diff_sparse_disk annotations. It seems I am overestimating memory requirements, which results in using less memory than specified with --mem-cap-gb

[karasikov]

Please apply .clang-format or make it more or less consistent with the code style in the rest of the codebase.

[marekkokot]

Thanks for pointing this. I configured my environment to use .clang-format file and reformated my changes. If something is wrong let me know.