Accept parsers and detectors from CLI.
Accept parsers and detectors from CLI.

- CLI options are plain string, so only out-of-box parsers and detectors
  can be accessed.

- Detectors CLI option looks like:

  ```
  --detectors=requireCallExression,importDeclaration
  ```

- Parsers CLI option look like:

  ```
  --parsers="*.js:es6,*.jsx:jsx,*.csv:csv1&csv2"
  ```

depcheck/depcheck,depcheck/depcheck