The sts modules count what goes through nginx's stream subsystem -- per
server, per upstream, per filter -- and serve the counters as JSON, as a
Prometheus exposition or as an HTML page.  They are the stream side of what
the vts module does for HTTP.

Two modules are needed and both are here: one counts in the stream
subsystem and owns the shared memory, the other answers the status
requests out of it in an http server.  One without the other reports
nothing.

This port only installs the module sources.  The modules themselves are
built by the nginx ports when their STS option is enabled.