Slider.js corrections and additions

Source code and documentation are not matching in Slider.js. 

#### Change 1:

On docs says:
>__initialStep__ - (number: defaults to 0) The step the slider will start at.

The default value in the source code was `-1`. 
This PR defaults to the `range` minimum, when set. 
Otherwise `0` as the documentation describes.

#### Change 2:

The `complete` event reads: *Fire when you're done dragging.* 
The `change` events reads *Fires when the Slider's value changes.*

As it is, these events are being fired (**[twice!](http://jsfiddle.net/tjBjF/)**) during initialize . 
This PR makes the initialize *silent*, not firing those events.

#### Change 3:
This PR also adds `move` event as suggested by @olvlvl. I think is useful since the existing `change` event is locked to the slider steps, which do not reflect the knob's drag position/movement. 
This closes #1198