Allow use of yargs .config()

[shaunhurley]

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Hi, been using this a lot recently, super convenient, hoped you might incorporate this little tweak to make it even more so!

Included the .config() option in the yargs parameter handling in order to allow parameters to be read from a config file specified with the --config command line option i.e. --config test.json rather than everything having to be entered on the command line every time.