Rename "format" to "output format"

I'd like to bring this into line with the terminology in the plugin system.

I think the way I will do this is:

In a minor release, add an --output-format command line flag and an outputFormat key in the config file
Make them do the same thing as --format and format
Mark --format and format deprecated in the changelog
Mark format deprecated in the JSON schema
Mark --format as deprecated using yargs
Log a deprecation warning to the console if either of those things are used

Then in the next major, actually remove format and --format

chris48s / v8r