Add draw.aaellipse

[mzivic7]

This PR adds draw.aaellipse function, with width and thickness options.
It is completely interchangeable with draw.ellipse in terms of arguments.
Algorithm used is adapted from Xiaolin Wu's general fast antialiasing algorithm, and is very similar to draw.aacircle.
Only notable difference: in aacircle, 8 pixels are drawn at once, but here, only 4, because ellipse has 2 symmetries. Because of that aaelipse has additional vertical drawing (aacircle has only horizontal but because of extra symmetries it is vertical at the same time).
It is added to docs too.

Sample code

import pygame

pygame.init()
screen = pygame.display.set_mode((512, 512))
clock = pygame.time.Clock()

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
    screen.fill("black")
    pygame.draw.aaellipse(screen, "red", [100, 100, 100, 50], 1)
    pygame.draw.aaellipse(screen, "red", [100, 160, 100, 50])
    pygame.draw.aaellipse(screen, "red", [100, 220, 100, 50], 4)
    pygame.display.flip()
    clock.tick(60)
pygame.quit()

[MyreMylar]

Well this looks good to me. The new algorithm performs better than the one in gfxdraw (which has gaps in it) and adds the filling functionality. Tested a variety of parameters locally and all looked nice and behaved how I would expect.

Can't find any problems with the code, not going to pretend I understand the intricacies of the algorithm for drawing, but it looks sensible from a look over and produces an output I respect. 👍

[mzivic7]

Note: before merging, correct versionadded in docs/reST/ref/draw.rst, if needed.

[mzivic7]

I moved ellipse and aaellipse functions bellow circle and aacircle, because aacircle is called in aaellipse and aa* functions should always be bellow regular one.

[Starbuck5]

I see holes around the edges of the ellipse in this test case.

import pygame
screen = pygame.display.set_mode((600,600))
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN and event.key == pygame.K_w:
            pygame.image.save(screen, "output.png")
    screen.fill("purple")
    pygame.draw.aaellipse(screen, "red", [100,200,300,400])
    pygame.display.flip()
pygame.quit()

[Starbuck5]

Other things I see.

• pygame.draw.aaellipse(screen, "red", [100,200,30,200000], width=0) crashes the app
• putting in a rect with negative dimensions leads to weird stuff being drawn
• if the width and the height are equal the surface being drawn on cannot be blitted in the future (you forgot to unlock it in this case)