feat(summary): use violin plot as summary image
feat(summary): use violin plot as summary image

Closes #7

japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs,japaric/euler_criterion.rs