Broken SAT link in Chapter 12: Collision Detection

[Iron-Smithy]

The external link explaining the Separating Axis Theorem (SAT) in Chapter 12 of the MonoGame tutorial is currently broken.

at: https://github.com/MonoGame/docs.monogame.github.io/blame/dd8c04ccb10a75da6664e14f6be2955638bd07ed/articles/tutorials/building_2d_games/12_collision_detection/index.md#L110

the URL: https://www.sevenson.com.au/actionscript/sat/

was moved to: https://www.sevenson.com.au/blog/sat/