Parse the command-line options.
@param definitions {OptionDefinitions[]} - to be passed to command-line-args
@param [usageSections] {section[]} - to be passed to command-line-usage
@param [argv] {string[]} - If supplied, this `argv` array is parsed instead of `process.argv`.
@returns {object}
@static
function getCli (definitions, usageSections, argv) {
  const commandLineArgs = require('command-line-args')
  const commandLineUsage = require('command-line-usage')
  const usage = usageSections ? commandLineUsage(usageSections) : ''
  const options = commandLineArgs(definitions, argv)
  return { options, usage }
}