LinkedList Refactor
LinkedList Refactor

- This PR incldues a number of small changes to make the API for the
  LinkedList class both easier to read, easier to override and hopefully
  easier to implement a subclass.
- Refactored a few methods to use Symbol#to_proc
- Added comments regarding implementation details so those who wish to
  subclass can do so easily

envato/rake,ruby/rake,envato/rake,ruby/rake