Added a separate QpidPmda.h header, and include guards.
Future-proofed pcp::pmda::instance handling.
Renamed the QMFv1 version of the QpidPmda class to QpidPmdaQmf1.
Renamed the QMFv2 version of the QpidPmda class to QpidPmdaQmf2.
Updated to use PMDA++ 0.3.3 in Travis-CI.