v0.6.0

Changes:

• Remove affinites from TSNE construction, allow custom affinities and initialization in .fit method. This improves the API when dealing with non-tabular data. This is not backwards compatible.
• Add metric="precomputed". This includes the addition of openTSNE.nearest_neighbors.PrecomputedDistanceMatrix and openTSNE.nearest_neighbors.PrecomputedNeighbors.
• Add knn_index parameter to openTSNE.affinity classes.
• Add (less-than-ideal) workaround for pickling Annoy objects.
• Extend the range of recommended FFTW boxes up to 1000.
• Remove deprecated openTSNE.nearest_neighbors.BallTree.
• Remove deprecated openTSNE.callbacks.ErrorLogger.
• Remove deprecated TSNE.neighbors_method property.
• Add and set as default negative_gradient_method="auto".