Add pre-commit hook to remove cursors.

[slendidev]

This PR adds a pre-commit hook specifically for *NIX systems to remove the cursor byte from all files under src/.

The reason why I chose python is because it is assumed that most *NIX systems already come with it pre-installed.

[slendidev]

It does not rely on a Python dependency if the contributor doesn't want to use the actual hook. This is totally optional. I mean you need to install the hook after all with the appropriate hook.