Release candidate

[tony-kuo]

New features:

• A search_exhaustive method in CellQuery which allows the user to forgo the kNN search and instead search cells based on a distance threshold and optionally a metadata filter to select for a given metadata profile.
• The query_coherence statistic, which measures consistency of query results between the centroid and cells that comprise the centroid, now has a random seed parameter.
• Various improvements have been made to the training modules to add more metrics to evaluate training.
• Various changes to utility functions to improve efficiency.
• Tutorials have been updated with new download links and analysis.