Error with commas in margins
This plugin is awesome, for starters. ;)

I'm on a Mac with German localization and therefore, the decimal separator is a comma and not a point. The grid options in certain situations come up with `0,0` by default, which causes an error if not corrected to `0` or `0.0` manually.

Maybe you can do some sort of parsing on the input, that would be great!

By the way…Sketch has the same problem, for instance when calculating widths etc.

![margin](https://cloud.githubusercontent.com/assets/61015/8801576/07b1aeac-2fbc-11e5-91fd-a55f9d973a98.png)
