v0.2.0

cellpypes has matured under feedback from colleagues. New features:

• use Negative Binomial instead of Poisson
• classify has knn_refine argument
• pype_from_seurat has parameter graph_name now (#17).
• you can pype Seurat objects directly into rule / feat without calling pype_from_seurat
• minor:
  • pype_code_template checks it's input is integer