[Feature Request] Add max-markers, snaps and step attribute

[roflcoopter]

Hi!

I have a light that i am only able to set to 0, 50 or 100%, and am wondering if you could add support for the paper-slider attributes max-markers, snaps and step? This way I can limit the slider to just these values.

I tried making a fork and implement it myself but i cant wrap my head around the structure of the files.