1. A vector is an entity that can be added to another vector and can be multiplied by a number. It is senseless to add two points or to multiply a point by a number.
2. In geometry, a vector is a translation or displacement; a point is a position.
3. Because some events are discrete. For example, when I click on a button, I am not interested in how many milliseconds the mouse is pressed; I just want to get one click event. If I type a word, I want to get just one character input for every key pressed.
4. Because assets are usually loaded only at application startup, or when a level is entered or exited.
5. The optional key_down_event, key_up_event, mouse_button_down_event, and mouse_button_up_event methods can be defined for the EventHandler trait. Such methods register in the model that they have been called (that is, that the corresponding events have happened in the time frame). Then, the update method checks and resets such settings in the model.
6. It is a set of shapes to draw. To draw...