Dynamic exporters for smartpireadout

[SuperQ]

Now that we've refactored the readout.go file a bit, the main loop is much cleaner.  I don't see a lot of utility to come up another interface, and then a whole bunch of different binaries to do their own interfaces.

For example, adding Prometheus support is not terribly complicated with the current single reader binary.

https://github.com/nDenerserve/SmartPi/pull/32