Expand and Improve Boost.Compute

by Roshan for Boost C++ Libraries

Implement a parallel version of some algorithms which are present in C++ STL and are missing in Boost.Compute. Improve the Random Number Generation aspect of the library by adding few extra distributions and a new engine. Test and benchmark all of the above adequately. Improve the performance of some of the existing algorithms by providing alternate implementations to the ones already present. Note that this will also involve benchmarking them first.