Add benchmarkAPIurl to config.sample: copy to config.yml!

To be able to submit benchmarks to our Google Spreadsheet, this
config setting must be in your config.yml file.
Add Submit Benchmarks button that sends data to Google Spreadsheets

This bundles up the data in the Average row of the benchmarks table into
a data object and submits it to a Google Web App, which receives the
data and publishes it to a public Google Spreadsheet.