PowerGenome/PowerGenome: v0.5.6

What's Changed This release primarily fixes a bug in the calculation of how many existing generating units are in each cluster. The number of units is used to calculate existing capacity, so in many cases the existing capacity would be 0. Update README.md by @gschivley in https://github.com/PowerGenome/PowerGenome/pull/204 Bug fix num units in cluster by @gschivley in https://github.com/PowerGenome/PowerGenome/pull/207 Full Changelog: https://github.com/PowerGenome/PowerGenome/compare/v0.5.5...v0.5.6