improve documentation
move initialization to MooX::Cmd::Role

* as discussed with Getty in #web-simple, let MooX::Cmd be a bootstrap
  loader only and modern implementations can do
  with "MooX::Cmd::Role";
* allow modify all initialization parameters via class _build_ functions
  (called in class context, but as method)
add some samples to role

author wants ('examples') x INT_MAX - unfortunately he gets only one