Specs: Ensure every API command is a subclass of Collmex::Api::Line.
Specs: Fix deprecation warning (has_key? -> key?)
Specs: Re-initialize RSpec3's preferred spec_helper and fix/clean up specs afterwards.
Specs: Improve coverage and some clean up.
Specs: Remove obsolete/duplicate code.
Use autoload instead explicit require.
Refactor Collmex::Api.parse_line.