Use well-known file for the config module

[francoiscampbell]

Is your feature request related to a problem? Please describe.
The CLI command feels verbose compared to other tools.

Describe the solution you'd like
Like make, invoke, and eslint, use a well-known filename, perhaps codewatch.py as a default config module filename. This would make the CLI simpler, with the potential for just running codewatch and nothing more. This is related to #12 in that the CLI could become `codewatch .

We could preserve the ability to specify the config module under a named CLI parameter, such as codewatch --config <path to config file>.

Describe alternatives you've considered
No major alternatives, this feels like either it's changed or not.

[noahnu]

Maybe codewatch.config.py or something of that sort?