[feature] custom config file location and name

[ngarbezza]

Is your feature request related to a problem? Please describe.

It's limiting that the configuration file has to be named .testyrc.json and has to be in the root folder. Some projects might use a config folder and/or a specific naming convention for config files.

Describe the solution you'd like

A command line argument to tell where to find the config file:

$ testy --config conf/testy.json <files>
# OR
$ testy -c conf/testy.json <files>

Describe alternatives you've considered

None

Additional context

N/A