Adds test coverage for NumberHandler

Hi Gavin:

I saw your note in the WIP pull request (#1), but I wanted to provide you with something useful anyway. I can't stand to see work left unfinished.

If you're set on only hiring a person as an official employee because that's the only way forward for RealHQ, then no problem, let's part ways and I hope you gain some small value from the work we've done here.

But if you're open to someone who interacts with the rest of the team as if they were a part of it (attending daily standups, interacting in the chatroom, and closely working alongside your other team members) and also carries with them the benefits of a strong process (demonstrated here), then I would love to explore where this can go.

You'll be able to not only enhance your team, but potentially improve processes to help ensure a bright, less stressful, future for RealHQ. It's a process I've seen work with teams up to 20 developers to great success. It's extremely similar to the process used by GitHub to build the tools bringing this to you now.

The process involves feature branches for all changes, backed by tests, and reviewed by other developers before being merged to `master`.

With a process like this, you can have the confidence to deploy multiple times a day, every day, which lets you put a bigger smile on the face of the real stars of the show, your users.

It goes beyond just being able to deploy often though.

Because if everything is developed in a feature branch and merged to `master` in a "squash merge" (Like you can see here `git merge --squash nh-feature-branch`), the history of commits in `master` become far more useful.

You can do a `git blame` on any line in the project and get a window into what has changed, and instead of seeing it attached to a commit labeled with something like `tweaks widget method`, you'll see a squash merge that contains the full, accepted, changeset with context and a link to the discussion in the pull request. Ideally, you'll include a link to your Pivotal Tracker (or other system) in the pull request too. Then you can trace a line of code all the way back to the conversation that spawned the need.

Just think about all of the duplicated conversations that a process like this can eliminate.

There is a lot more to it than that, but I want to let you know again, we're interested. We're willing to play by your rules (within reason). We want to feel like a part of your team.

If we give things a shot and it doesn't work, then we'll part ways, but you'll get to keep everything you learn from me and my (small) team as you forge a bright future for RealHQ.

Let me know if you're open to having us work as an extension of your team. We'd love to help.

Thanks!
Nick
nhance@reenhanced.com
Cell: 215-804-9408

P.S. All of the work we've done here is yours to keep. Please feel free to merge it and use it as you see fit.

---
This adds missing tests to validate that the mixin functions as expected.

Closes reenhanced/real_hq_shared#1

LGTM given by: @codenamev

```
Squashed commit of the following:

commit d79812b64340efb95c7160db67c4d32259358d10
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Wed Jun 5 14:25:14 2013 -0400

    Refactor to use initializer

commit b139a79fe0679161ec7dbdb5e0481185d486c10a
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Wed Jun 5 14:17:14 2013 -0400

    another small update

commit 19f4aa4a8db60d1467ca329f01a5baabdcb61104
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Wed Jun 5 14:11:02 2013 -0400

    pull request updates

commit 76de0c49bc1029bd507c166efaa1702ab5e13b39
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Wed Jun 5 10:04:53 2013 -0400

    finishes tests

commit 919b8513e6f2da34d14a1c555ac096f7471eca63
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Tue Jun 4 18:11:16 2013 -0400

    AttributeMethods isn't required after all

commit 4ee3cc9eee12aa98cb8de1f280b9a55908262d6c
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Tue Jun 4 18:10:25 2013 -0400

    Adds missing files. I always forget that

commit db2257b1f032c7eb13baa020293fa287142a2e03
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Tue Jun 4 18:00:02 2013 -0400

    Phone numbers and a start on currency_numbers. Will finish this up tomorrow for maximum first impressions.

commit 28a3e43e6d0e0155beb7101bd83eb1aacaf37686
Author: Nicholas Hance <nhance@reenhanced.com>
Date:   Tue Jun 4 16:22:05 2013 -0400

    NumberHandler.sanitize_phone_number tests
```