Charts: automatic min estimation
Created originally on Bitbucket by datacompboy (Anton Fedorov)
Currently min is hardcoded to zero. Need to fix Chart._compute_min_max to recalculate .min if it None
Created originally on Bitbucket by datacompboy (Anton Fedorov)
Currently min is hardcoded to zero. Need to fix Chart._compute_min_max to recalculate .min if it None