Renames: 		 toSliderValue => toValue 		 updateSlider  => updateKnob Move setSteps code to its own function
Renames:
		 toSliderValue => toValue
		 updateSlider  => updateKnob
Move setSteps code to its own function

wancharle/Leaflet.zoomslider,kartena/Leaflet.zoomslider,kartena/Leaflet.zoomslider,wancharle/Leaflet.zoomslider