Adds a new queue manager connect option: use_system_connection_data

It is used when you want to initialise a client connection, but you want
to obtain the connection_name and channel_name from one of the system
configuration methods. These being: mqclient.ini file, MQSERVER ENV
variable or CCDT.

Sample usage:

WMQ::QueueManager.connect(q_mgr_name: "*SOME_Q_MGR", use_system_connection_data: true) do |queue_manager|
  ...
end
update use_system_connection_data explanation to make it clear that MQSERVER is an ENV variable
adds documentation for the use_system_connection_data to the queue manager singleton connect method comments
Merge pull request #7 from Ferocia/master

Add a new queue manager connect option: use_system_connection_data