`normalize` should normalize link targets

[agarwal]

I can't remember if this was previously discussed, but our current normalize doesn't normalize link targets. I feel like it should. The benefits would be:

• The implementation of equal would be simplified. We could simply call Pervasives.equal after normalizing the two paths. Thus, we could delete equal_normalized and equal_item, which right now do nothing more than Pervasives.equal except for recursively normalizing link targets.
• We could do the same to implement compare, which we currently lack and thus cannot easily apply Comparable.Make.

On a related note, we should avoid the wildcard pattern in equal_normalized. It would be only 1 more line of code to be explicit.

Once this is done, we should include Comparable.Make.

[pveber]

I implemented compare, but I think using Comparable.Make is not possible due to type parameter in Path.t. Only possibility would be to provide the four variants, should I do it?

[agarwal]

Four variants isn't ideal. Let's hold on this.

[agarwal]

Let's decide to not call Comparable.Make. Users can call themselves for now in the cases they need it. So closing this issue.