Create a new button object with a specific mnemonic (accelerator : it is a key combinaison for a best accessibility)
Crée un nouvel objet bouton possédant une étiquette.
_channel_ : Chn : any channel
_label_ : S : the label of the button with a mnemonic (any string). This mnemonic must be an underscore and any charactere.
Return : ObjGtk : this object if success or nil if an error occurs
typeof button = ObjGtk;; fun main()= _showconsole; set button = _gtkButtonNewMnemonic _channel "B_outon"; ...
