Optimize render and zoom

[raczben]

Feature request - Optimize render and zoom

Current implementation redraws all bus (aka. bit-vectors) at all zoom-end event. The problem is that d3's data are identified by their order in the array, while wave would require it as value.

Another problem is that the lowest level code (drawing the signal elements) gets the same values multiple times, which can be optimized. I suggest to use less feature of d3 and implement custom functions for the lowest level drawing.