Improved Nugrant::Config class implementation
 * Methods merge and merge! are now supported and tested. They are of
   not much use since instance variables are simply copy over the other
   but could prove useful in the future.
Improved Nugrant::Bag implementation
 * Correctly implemented dup().
 * Correctly implemented and tested plain merge.
Added possibility to change Bag's config object after creation
Implemented parameters merge
 * This fix bad implementation of Vagrant config object which was not
   merged correctly with other vagrantfiles causing ripple effect
   of command in namespace `vagrant user` to not have the correct
   final config.user object.
 * Parameters merge is always performed using an array replace
   strategy.
 * Added possibility to pass custom merge options to Bag.merge method.
Bumped to 2.0.0.rc1