Merge pull request #9 from alfredxing/remove-core-exts

Replace usage of monkey patches with modules
Remove String and Hash core extensions
Merge branch 'remove-core-exts' of github.com:jekyll/classifier-reborn into remove-core-exts

* 'remove-core-exts' of github.com:jekyll/classifier-reborn:
  Replace usage of monkey patches with modules

Conflicts:
	lib/classifier-reborn/bayes.rb
	lib/classifier-reborn/lsi.rb
Wrongly replaced calling of ContentNode.word_hash