Enhancement request: add "initialZoom" attribute

[rustyx]

Please add an "initialZoom" setting which would allow to scale the SVG in relation to the SVG's user space only.
My SVG needs to be scaled down by 4, the only way to do that is to define viewBox, but I also want to occupy the whole browser window, so I set width to 100%, in this case the SVG is scaled based on browser's window size, whereas I want it to scale in such a way that 1px always corresponds to 4 units in my SVG's user space.
A setting "initialZoom":0.25 (or maybe a better name is "initialScale") would be really useful in this case.