Add Chapel versions of matmul and nqueen

[mppf]

This PR adds Chapel ports of the C matmul and nqueen benchmarks. These should have competitive performance with the C versions (at least, they do on the systems I have tried them on).

This PR also includes a few alternate versions of nqueen. (These can be removed if necessary before merging).

Please reach out if you have trouble getting these to compile and run on your system.

[mppf]

@attractivechaos please let me know if I can do anything to help towards getting this PR merged, thanks