Improve code to look up info from a remote site. Write entries into the composer.json in the current working directory, if one exists.

Respect --base option, to start with a different base composer.json. Add an --output option, to write the resulting composer.json file to a specific local file.

Switch to using packagist.drupal-composer.org instead of drupal-packagist.webflo.io (currently these are aliased to the same site).