Disable implicit rules.

    Implicit rules were preventing the '.deps' directory
    from being created correctly. They also might have caused
    sporadic failures due to a missing dependency on generated
    headers.

    This kills them. Explicit is better than implicit.
Add benchmarking runner and makefile.

    Now you can do 'make bench', and see how fast Myrddin runs. Or
    at least the integer sorting bit.

    TODO: expand this so that you can see how it compares to previous
    results, and add benchmarks.