This also replaces all the assembly that previously used the AT&T style
with the (in my opinion) superior Intel syntax.

I tried prepending `.att_syntax prefix`, but that did not work...

I didn't think it'd be this useful first, but thank god for `cargo fix --edition`!

https://github.com/BurntSushi/rust-memchr is supposed to be a whole
lot faster :)

This reverts commit d6a5b395.