Update to work with 20.x versions

Also switch to rebar3 for builds.

Bump version of afunix

To one that builds under rebar2 and rebar3

allow www files from priv directory of module

update gitignore with some rebar3 things

Refactored lwes forwarding backends.

Instead of having almost identical code, they now both use the
mondemand_backend_lwes_worker as their worker mod.  This does mean
that additional configuration is required on the clients in order
for them to work in the same way, but it should be minimal.

Release 6.0.0

Refactor of how dispatching works to remove gproc

Eventually, I feel it should all be refactored so that there is no
intermediate passing of the event and instead new processes are spawned
which shuttle things along.

Fix to remove spikes on initial values after restart

When the server is restarted with the previous logic, you might get a
large value for a counter, then return that as the gauge value since the
values were defaulting to 0.  By changing the defaults to undefined and
have a clause to check if value2 is undefined, we ensure that we have to
have seen 2 values before we calculate the difference.  This removes
initial spikes on server restart and instead you just get 0 values for
that minute.

New version

fix for floats as trace id/owner