feat(LRUCache): initial incomplete implementation

I'm just committing whatever work in progress I had going on.  This will
be on hold until I find time to get back to it.
feat(LRUCache): remove gratuitious complexity
docs(LRUCache): add TODO

Ref: issue #188
feat(filter): new orderBy filter

TODO:
- support functions for the expression parameter?
- support a list of expressions

Ref #146
feat(filter): limitTo filter

Closes #143
fix(filter): don't support string limits in limitTo filter

In AngularJS, the `limit` expression can be a string that is evaluated a
second time.  I don't see the use for it.  Removing.

Closes #143
feat(filter): orderBy filter now supports lists(of)/expressions/functions

Closes #146
feat(mock): implemented mock timer

Closed #163
feat(orderBy): add docs + update tests + minor changes

Closes #146
chore(mock): remove excessive logging in MockHttpBackend