[FEAT] Support for K_KP_ENTER:

[Naturalbornhippy]

It happens to me while playing/coding that i press the "wrong" enter key - so i think it would be good to add the 2nd enter key (at least if you have a key pad)

Describe the solution you'd like
I want to change this line:
if event.type == pygame.KEYDOWN and event.key == pygame.K_RETURN:
to
if event.type == pygame.KEYDOWN and (event.key == pygame.K_RETURN or event.key == pygame.K_KP_ENTER):

You could go with a 2nd if statement, but i think we can still understand this line.

Should i create PR for this?

[Naturalbornhippy]

Decided to integrate it into #70