Version 0.2.2

• Fixed heatmap plotting via updated plot_heatmap for cases with blank
  results and only one unique non-blank value (#22).
• Added check in analyze_dataset for locus name mismatches between dataset
  table and locus attributes table (#21).
• Added check in prepare_dataset for missing data directory (#20).
• Added check in prepare_dataset for zero-detected-files case.
• Added check in load_dataset for missing data files.
• Added check in full_analysis to warn if any input data files are
  completely empty.