Changes to memory management of handlers

Changed

• Recent addition of basic_config() (see previous release)
  introduced an ambiguity for memory management. The underlying
  design from Python is based upon garbage collection and reference
  counting. To solve this problem there the user can now either
  specify a HandlerVector or a HandlerPtrVector (but not both) If the
  former, pFlogger will copy the handlers into its internal storage.
  If the latter, pFlogger will only retain a pointer reference to the
  user actual argument. In that case, the user is repsonsible for
  maintaining the handlers until pFlogger is finalized and ensuring
  that any locks are freed.

• The argument to Logger::add_handle() must now have the TARGET
  attribute. pFlogger will only maintain a pointer to that target.
  This is to be consistent with the above strategy.

Fixed

• Implemented workaround for ifort 18.0.5 that became necessary after
  the changes above. Only impacted unit tests.