Various fixes for the documentation

[PeteHaughie]

I was working through some old example from Dan Schiffman's Nature of Code and realised there was no random() description which returns 0.0 – 1 (non inclusive) as was mentioned in his example sketch here: https://github.com/nature-of-code/noc-2-processing-port/blob/main/chapter0/Example_0_3_Random_Walk_Tends_To_Right/Example_0_3_Random_Walk_Tends_To_Right.pde

Additionally there were duplicate x and y components in the PVector.set() parameters