Change name of int_input to be lever specific
* Change error messages
Change method name one more time
* Move print statement into interface function
Prevent Gates._switch from being called with None
* remove weird hack that decremented moves
* blocked bad input from reaching ._switch or .moves
* select_lever returns 0 instead of None
Extract in_range functionality to new interface method
Move display.print_moves into print_gates
* capitalize "taken" so that it looks nice
Rename interface module to user_input
Update README with hints + link to Indiana Jones