Fix top level requires

Fixes any place that did `require 'rbhex'` and does `require 'rbhex/core'`.


To reproduce the error
------------------------------

1.  Checkout this repo (or the original from @ChrisArcand)
2.  On the master branch build the gem by doing the following:  `gem build rbhex-core.gemspec`
3.  Install the gem:  `gem install rbhex-core-1.1.0.alpha2.gem`
4.  Try running one of the examples:  `ruby examples/alpmenu.rb`