Move all code under an Hbc:: namespace

* convert existing Cask:: namespace to Hbc::
* move Homebrew-fork code under Hbc::
* move freestanding classes such as Tty and TopologicalHash under Hbc::
* recast HOMEBREW_CASK_ constants as HBC_
* modify our Homebrew Formula for backward compatibility
* devscripts and dev docs

developer/bin/bump_version

@@ -14,9 +14,9 @@ require 'rubygems'
 ### configurable constants
 ###
 
-VERSION_FILE          = 'lib/cask/version.rb'
+VERSION_FILE          = 'lib/hbc/version.rb'
 VERSION_PAT           = %r[\d+\.\d+\.\d+]i
-VERSION_CONSTANT_NAME = 'HOMEBREW_CASK_VERSION'
+VERSION_CONSTANT_NAME = 'HBC_VERSION'
 
 ###
 ### methods