Prepare module to be published to npm

It would be really great if backbone.subroute was published on [npm](https://www.npmjs.org/). I made all the necessary changes in order to make it work. If you need help, [this doc](https://www.npmjs.org/doc/misc/npm-developers.html) should help you with pretty much everything. If you need any other help, I can probably answer any questions you have.

---

**Changes:**
- Added `.npmignore`
- Fixed license url 
- Changed main attribute to correct file (also [fixed here](https://github.com/ModelN/backbone.subroute/pull/33/files#diff-b9cfc7f2cdf78a7f4b91a753d10865a2L25))
- Move backbone from `dependencies` to `devDependencies` (explained below)

---

I moved backbone to `devDependencies` because backbone should always be a peer dependency. If you declare it, then something like browserify will require two separate backbones (one from their app, the other from your module), which you really don't want.

---

If you need anything else in this PR, please let me know. Thanks