Add smooth(), stroke_weight()

[igayara]

I'm translating Nature of Code to p5 and I'll list the missing features as I come across them.

Chapter 1:

• smooth()
• stroke_weight()

p5 version: 0.3.0a2

Python version: 3.6.2 Operating System: Windows 10

[GOMMB]

I also would like to see stroke_weight(). I tried to implement it using glLineWidth() and it works if you want everything in the frame to have the same weight, but it doesn't work to have objects with different weights in the same frame. I believe this is because you are drawing entire frames at the same time, and I wasn't able to figure out how to work with that.