docs: Fix a few typos

[timgates42]

There are small typos in:

• PyDark/engine.py
• PyDark/net.py
• PyDark/vector2d.py
• README.md

Fixes:

• Should read indefinitely rather than indefinetly.
• Should read whether rather than wether.
• Should read separates rather than seperates.
• Should read variables rather than varaibles.
• Should read representation rather than representaion.
• Should read receive rather than recieve.
• Should read inputted rather than inputed.
• Should read controls rather than controlls.
• Should read collision rather than collison.
• Should read available rather than avaialble.
• Should read achieves rather than acheives.
• Should read achieve rather than acheive.

Semi-automated pull request generated by
https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md