Detect left recursive parsers making no progress

[nikabyn]

Implementation of #303
Adds a debug panic for left recursive parsers without memoization.

[zesterer]

Unfortunately, I don't think the changes in this PR are sufficient by themselves. For example, I'm pretty sure any mutually recursive pattern will not be caught, such as this:

recursive(|a| {
    recursive(move |_| {
        a
    })
})

I think unfortunately something more substantial is required, like piggy-backing on top of the memoisation hashmap.

[zesterer]

Now being worked on in #371