Add UMD wrapper, remove separate AMD version

#### Resolves #43 

**Changes:**
- Remove AMD version
- Add UMD wrapper

**UMD Details**
- AMD
  - return `Backbone.Syphon`
  - `Backbone.Syphon` is defined
- CommonJS
  - `module.exports = Backbone.Syphon`
  - `Backbone.Syphon` is defined
- Browser
  - `Backbone.Syphon` is defined

**Note:** Since jQuery was always a hard dependency (references `window.jQuery` directly and required `jquery` in amd) its staying that way for now. That will be addressed separately.