Use test262 data to generate page to show our conformance

[jasonwilliams]

Boa generates TEST262 data on every PR.
It then dumps out some JSON files which chart how conformant we are compared to the test262 suite.

Currently we do nothing with this data.
It would be good to it to our gh-pages branch and use it to generate a static page.

You can test this locally by running.
cargo run --release --bin boa_tester -- -o gh-pages/test262
then inspecting the JSON output.

I'm easy on charting library.

1. We should have a new github action that runs test262 (weekly?) and generates data
2. Use that data to generate a page on github.io

[Razican]

This was already implemented.