refactor operations into private methods
refactor operations into private methods

This change is in preparation for supporting subscriptions.  The
generation of the next correlator id has been refactored into a
independent method as well as the code required to open a service.

flojdek/blpapi-http,fyquah95/blpapi-http,bloomberg/blpapi-http,bloomberg/blpapi-http,flojdek/blpapi-http,fyquah95/blpapi-http,flojdek/blpapi-http,flojdek/blpapi-http,bloomberg/blpapi-http,flojdek/blpapi-http,fyquah95/blpapi-http