* Work stealing now works correctly.
* A thief attempts to steal (victim's work count / number of threads) amount of work per steal operation.
* Before the threads are started the entire work-load is given to thread 0. The other threads become thieves to retrieve a work-load.

* Changed output to colour ppm which displays a different gradient for each thread. This illustrates which thread did which lines of work and how much work is being balanced. This has some impact on performance and
  also limits the size of the matrix much more than the grey-scale version. The sequential version needs to be brought inline with this version to give any good grounds for comparison.