holds the single instance and triggers initialization

Declaration :

• Uml : static, - theApp_ : Appconfig
• C++ : private: static Appconfig theApp_

perform initialization on first access.
A call is placed in static initialization code
included in lumiera.h

Declaration :

• Uml : - Appconfig() :
• C++ : private: Appconfig ()

Declaration :

• Uml : static, - instance() : Appconfig*
• C++ : private: static Appconfig* instance ()

access the configuation value for a given key.
@return empty string for unknown keys, else the corresponding configuration value

Declaration :

• Uml : static, + get(inout key : string) : string
• C++ : public: static string get (string & key)