Added options to allow customization of fill_color, fill_opacity - and fixed minor bug with stroke_weight option

Nice library, just what I was looking for! Thanks for posting it on github. 

This pull request includes a few very small tweaks: 
- there was a minor bug in the stroke_weight option, so it wasn't working. 
- I added the option to allow customization of the fill opacity and fill color. 

Thanks again - 

Ben