Basic spec for grid testing

[vsoch]

• Add grid section: grid is to define one or more environments (Docker bases and other params) optionally with some way to install dependencies, and then tests are automatically run over environments.
• Add range template for args, so one variable can be run across a range of values.
• Add optimize section: given a set of environments and ranges, should be able to evaluate results for some value / metric.
• Web results interface should visualize tests and “grid” of results for each combination, optionally colored based on metric (red/green for pass and fail or spectrum for color).

[vsoch]

This is done.