Consider making all shape arguments keyword-only?

[tusharsadhwani]

Essentially for three reasons:

• circle(x=100, y=100) is easier to explain than circle(100, 100) for first time learners, as it's clearer that x and y values are being assigned
• Having code like circle(100, 50, 20) can confuse beginners, as they could misremember the order of args
• circle(50) and circle(r=50) look very similar but result in completely different results