Allow deep zooms

[rosslh]

It would be great if you could zoom in further. This is a challenge because floating point numbers have limited precision. Other fractal viewers have gotten around this by using arbitrary-precision arithmetic.

This might actually be impossible due to limitations of Leaflet.js. So to resolve this issue, please either implement deep zooms or verify that it is impossible with Leaflet.js and add some documentation to the readme explaining why the site does not support deep zooms.