Add remarkable benchmark

[danbulant]

I was interested in seeing how markdown-wasm compares to remarkable, which was made to improve marked - not only to improve speed but also add plugins. Their benchmarks say over 3 times speed increase over marked (which if accurate would mean it's faster than markdown-wasm), in reality it's less than 2 times on average.

This pull request adds remarkable to the benchmark suite (with their default settings) and updates rendered images to include my results. You likely want to run it on your macbook to have the results from your macbook as stated in README.

I have 3.5 GHz AMD Ryzen 3 desktop, 16GB RAM running Manjaro 5.10