Docs for arc: origin -> center

[soegaard]

Issue description

The description has the following sentence:

"The origin of the arc's ellipse may be changed with the ellipseMode() function. "

This should be:

"The center of the arc's ellipse may be changed with the ellipseMode() function. "

The word "center" is used for ellipses. The word "origin" is used for coordinate systems. Reference: https://en.wikipedia.org/wiki/Ellipse

URL(s) of affected page(s)

https://processing.org/reference/arc_.html

Proposed fix

Replace "origin" with "center".