Fixed a bug in groupby op. Added support for storing results as binary files.
Speedup of sort strings in 2 - 3.5 times.
For strings length is a multiple of two speedup in 2 - 2.5 times, for multiple of four in 3 - 3.5 times. (Speedup through accelerate of comparison of static strings.)
Merge branch 'master' of github.com:antonmks/Alenka into optimize_sort_strings