Import all Julia benchmarks from benchmarks game site into this repo

[non-Jedi]

That way we can compare programs here to those already submitted

[SimonDanisch]

I added the C++ examples manually: https://github.com/JuliaPerf/BenchmarksGame.jl/tree/sd-cppbench

[non-Jedi]

Supporting C++ as an additional language for comparison is a separate issue we should track in #34. For the record, doing so would be annoying but is still probably worthwhile in my opinion. :/

One option here would be to add the benchmarks-game repo as a submodule and then unpack the zip with the benchmark programs to a temporary directory as a step in run_benchmarks.jl.