planemo lint multiple

Would be good to have an option so planemo does not stop at first lint error when running lint on multiple paths.

Start at the planemo lint command entry point and trace how multiple paths are processed and how the first lint error stops execution. Done means an option allows linting all supplied paths and reports their errors instead of stopping at the first one; add or update tests for multiple paths if the existing command tests cover this behavior.

Written by the indexing model from the issue text.