Consider using emacs-memoize to speed up stuff

[Fuco1]

https://github.com/skeeto/emacs-memoize

We have options to cache by buffer content which should be bloody amazing when it comes to navigation (sometimes we do the same checks multiple times so this should really work very well).

However, we would have to do some changes to the API to express everything with arguments so that the memoization makes sense (i.e. (sp-get-thing) can not be reasonably memoized if we don't know the context).

So this might actually get trickier than it sounds :D

What I think will be necessary is to split the inner parts of the navigation functions out in a "pure function" kind of way that can be cached and the outer APIs will provide all the necessary arguments.

But then we don't really even have anything like formalized API... This project needs so so much love! :heart: