In Arg Parser: Moved option backpointer to _arg_parser struct
Added mutex to option struct using compound literals.
Added functions for mutual exclusion (Mutex) of options.

Implementation is efficient (linear) in number of options given on cmdline.
I added a new struct  _ap_Mutex_state and several functions which handle mutex.
Evaluating mutex in separate contexts is possible by initializing several _ap_Mutex_state structs.
Incorporated mutex of options into controller.

Mutex in context of endpoint and flow is now possible.
Merge pull request #133 from erzb5e6f65/Mutex7

Mutex