* version 0.1 - Initial release.  main tsne function included.
* version 0.1-1 - fixed misc. documentation omissions.
* version 0.1-2 - using an initial configuration parameter automatically places the tsne in the 'late stage' mode, which is mainly focused on small scale adjustments.
* version 0.1-3 - fix a broken gain equation, and made distance matrix checks more reliable
* version 0.2-0 - align preprocessing and optimization with reference implementation: replace whitening with standard PCA, change momentum switch to iteration 20, use vectorized gradient computation