Support for extended octet string groups 114 and 115

[thomas-rajan]

To start with we are looking for support in DNP3 master since our intial plan is to integrate the library with DNP3 master gateway.
We have older version sensors in field that uses object groups 110 and 111. Also we have newer version of sensors using object groups 114 and 115.

[jadamcrain]

These were actually added to the standard as a technical bulletin in response to the DNP3 vulnerability I was telling you about with "zero length octet strings".