legacy internal and client support for Menlo

 Menlo::Legacy is a package to install Menlo::CLI::Compat which is a
 compatibility library that implements the classic version of cpanminus
 internals and behaviors. This is so that existing users of cpanm and API
 clients such as Carton, Carmel and App::cpm can rely on the stable features
 and specific behaviors of cpanm.