Allow stacked bar chart segment spacing to be adjusted
Allow stacked bar chart segment spacing to be adjusted

By default, Gruff puts 1px spacing between each segment. This commits allows
that number to be adjusted.

vigetlabs/gruff,MentalPower/gruff,jbcden/gruff,innoq/gruff,jrmhaig/gruff,isozaki/gruff,topfunky/gruff,iox/gruff,philipgiuliani/gruff,topfunky/gruff