Use initWithCoder: instead of awakeFromNib

When configuring an `SMPageControl` from inside a Storyboard or XIB file, the developer might want to use _User Defined Runtime Attributes_ to configure the instance. `awakeFromNib` is called after those attributes are evaluated by the nib loading system, effectively overwriting the attributes defined in the Storyboard or XIB file. Therefore, `initWithCoder:` is the more appropriate location to perform the initialization.

![Screen Shot 2013-02-08 at 10 55 23](https://f.cloud.github.com/assets/161041/139045/aaa24214-71d9-11e2-98ca-52d39b9c7763.png)