Need modbus private function support

[stevesneed]

A native Pascal lib is great, would let me eliminate using the FieldTalk modbus DLL, but it's missing a critical capability: supporting modbus "private" or "user" functions (function codes $41..$48 and $64..$6E) as defined in the spec. I have to communicate with proprietary devices that use private functions for device identification, firmware updating and specialized data. Please add this support.