Add generic clustering algorithm, use in wifi clustering, cc #27.
Add filter for too-similar BSSIDs in queries, cc #27.
Add tests for BSSID similarity filtering, close #27.
Make magic constant '2' more explicit.
Move BSSID similarity filter to after database query, to improve hit rate.
Move length check to post-filter, missing hunk from previous commit.
Move cluster_elements from util.py to to service/locate.py
Use different lat/lon for different wifis in BSSID filter tests.
Use more efficient BSSID hex->byte split.
Add autofunction entry to docs for cluster_elements.
Add changelog, refs 27#.