Improve the merge history reordering for nnchain etc.

fix self-pairing in evaluation being inverted (and change default to false, too)

additional reference for cover trees

adjust boundary condition in ALOCI, did not affect test

bug fix in ALOCI

unnecessary inheritance

Avoid NPE in kd priority search

Indexed Boruvka versions

Improvements to indexed HDBSCAN

code cleanups for Searcher HDBSCAN

Searcher HDBSCAN

Improvements to buffered RSSL.

Cleanups/Improvements to HSSL, RSSL, INNC

code cleanups and unification for *SSL

Fix handling of duplicates and merge history.