Attach shipit.* variables on global init

[Sija]

Otherwise it's not possible to use 'em from tasks invoked out of deploy cycle.
Example below:

shipit.task('npm:build', function () {
  return shipit.remote('cd ' + path.join(shipit.releasesPath, shipit.releaseDirname) + ' && npm run build');
});

No way to run shipit deploy npm:build since shipit.releasesPath and friends are unset at that point.

[timkelty]

Agreed! Can you make PR?

[gregberge]

@Sija yes PR welcome