created unit tests for TagSifter.
removed pry references
moved unit test into seperate folder.
moved debugging_test to unit test folder
removed dependence on RubyBBCode.tag_list.  One less method required.
fixed comments and small things
moved bbtree_to_html into BBTree which chains into TagCollection wherein bbtree_to_html logic now resides.
cleaned out some unused and wrong code
renamed variables/ cleaned unused code.
Renamed the module inwhich @@tags were stored to be RubyBBCode (that's ok, right?).  Also moved the tag_list method out of ruby-bbcode.rb and into tags/tags.rb because I feel like it's not a valueable method but I could be wrong.
rewrote test to passing
ATTENTION:  refactored some code that I didn't exactly know what it's use cases were.  The method 'determine_applicable_tags' needs to be commented by code owner.
ATTENTION:  the ruby convention for '?' is to reserve them for methods which can only return true/false.  I recommend you manually do something to depricate the old method but don't remove it incase people relying on your code are using it.  Let it sit a while since it's no biggy.
moved escape_html code into tag_sifter
Removed my regex notes
cleared old comments and broke function up that was nested too deep and bore two responsibilities.
refactored tag_collection to be smoother.
Comments and order of things