update benchmark docs

I have figured out a script to "update the docs" for json benchmarks. https://github.com/sdarwin/json/tree/update-docs-2 . However, now hesitant to submit a PR because of how the system is functioning. Currently, in the json/doc/images/ directory are benchmark images consuming 1.3MB. An update to those images will increase the size of the git repository by 1MB, and thus boost by 1MB. Each time the images are updated it happens again. Maybe json boost docs should display fewer benchmark images?