English fixes/improvements to the comments

This PR contains a bunch of English fixes for comments in the code.
A bunch of the filters had incorrect copy/paste comments from the other filters, so I fixed those too.
I also rename one variable in a separate commit, it looks unused anyway.


I've been playing with pixi, thinking about using it for the global game jam this weekend. These were bugging me :-)

I haven't updated anything in the docs dir, it looks like something builds it.