set_key_symbol
Description:
Sets the key symbol of this.
Parameters:
| this | 
           a Event of type KEY_PRESS or KEY_RELEASE  | 
      
| key_sym | 
           the key symbol representing the key  | 
      
Sets the key symbol of this.
| this | 
           a Event of type KEY_PRESS or KEY_RELEASE  | 
      
| key_sym | 
           the key symbol representing the key  |