Prefix events to prevent conflicts between commands and options

[ajfranzoia]

Prefix internal command events with 'command:' and options events with 'options:' to prevent conflicts between equally named commands and options (both user and plugin options, like --version).
This fixes #471 as well.

[roman-vanesyan]

LGTM

[yausername]

Shouldn't this be added to the README? It is not documented anywhere.
I was wondering why this isn't working

program.on('verbose', function () {
  console.log('reached here')
})

[roman-vanesyan]

Yes, It actually should be documented. Feel free to send a pr 👍