Dlang merge sort implementation.

How to test: `dmd mergesort.d mergesort_test.d -w -unittest -release && ./mergesort 1000000`
If you want to track array state on each step compile with -debug flag.
Merge remote-tracking branch 'upstream/master'
Merge pull request #262 from 3Hren/master

Dlang merge sort implementation.
Merge pull request #263 from jcla1/master

Added Sudoku solver in Prolog, from 7 langs in 7 weeks.