Add CLI option for outputting configuration

[src-code]

It'd be helpful if the CLI could output the config file generated during parsing, either in addition to the CSS (aka a sidecar) or in lieu of CSS. The file could be named similar to the value of --output, so like:

atomizer -c base-config.json -o myatomic.css *.html

Which would generate:

myatomic.css
myatomic.config.json

Or, we can have a new flag for config output which is like -o|--output and takes a filename.