slider: support floating values, set number of decimals

For the needs of a math project, I had to modify slider to support floating values. It was rounding everything but I needed a two-decimal precision.

So I modified the source code and now I contribute it.

Basically, I added the functions "round" and "parse", and used them instead of "Math.round" and "parseInt".

I tried to stick with the coding style. The attached patch is in git format. I'm not confident with the format you expect for subversion. Just tell me so.

This is a ticket for the slider widget, but I didn't find it in the component list.