Added zoom to domain function. This allows to zoom to a given domain programmatically.

Added id in config, reason for this is that when connecting two EventDrops chart, it is very handy to have the id in the svg element the zoom is happening in.

Added the option to restrict panning (dragging behaviour) to the initial date range. So if the date range is from 2010 to 2012, it is not possible to pan to say 2009.
If the minimumScale is less than 1, it is possible to zoom out, however panning will be disabled so that it is not possibel to pan to say an earlier date.
ZoomToDomain function will ignore this (this is default D3 behaviour).

As we expect the dates to be already formmatted, I don't think it is neccessary to cast them to dates again.

Added optional arguments to zoomToDomain to allow for transition.

Removed id as this is simple to add manually.
Chnaged to restrictPan to restrictpan so it could be referenced in MD file (if someone knows how to reference in uppercase, please change).
Added in a check to see if _zoomToDomain is defined as function, if not then throw error.
Renamed zoomObject to zoom as it is more consistent with other D3 example code.
Zoom is now zoomFactory.
Removed unused code in test for index.
Changelog, configuration doc and Readme updated.