Simple pv

Reimplement the simple_pv interface to directly do a EPICS pcas server.

Previously the simple_pv library had provided a pipe to serialize framed json data to as a way to export debug information. Then an external process dc_cas.py would read from the pipe and reflect the data into EPICS. This is a reworking of the code to remove the external process and provide an interface to export int and string values into EPICS.

* Removes dc_cas.py
* Removes the old simple_pv.c
* Adds in a simple abstraction around an EPICS pCas server (C and C++ interfaces provided)

This removes the need to run another process on the FE systems for epics information.