Prompter - Add a CommandProcessor property to handle the command

[lastunicorn]

The CommandProcessor property must be of type ICliCommandProcessor. It should have a Process method that will be called immediately before raising the NewCommand event.

Update Wiki documentation.

[lastunicorn]

In the end, when the user types a command, I implemented the following steps:

• raise the NewCommand event;
• search for an item with the same name as the command (from the list of known items of the prompter) and, if found one, executes it;
• if no item fond, raise the UnhandledCommand event;
• and if the command is still unhandled, trey to execute the UnhandledItemCommand (it is a IPrompterCommand) that, by default will tell the user that the command was unhandled.