Update controls for accessibilty

[collinstommy]

svelte-paginate could be more accessible by making a few small changes.

1. Update the <span class="option"> to be a <button> (remove default styling)
2. Add aria-selected=true to the button that matches the active page
3. Add an aria-label to the buttons e.g. Go to page 1
4. Add a role and label to the container: <nav role="navigation" aria-label="Items Navigation">

3 & 4 could be passed in as props.

@TahaSh I can create a PR if you agree with these proposed changes?

For context, I use svelte-paginate on my site: http://aoelibrary.com/. I'm doing some work to make it accessible at the moment.

Repo: https://github.com/collinstommy/aoe-library

Thanks for making this package. It saved me a lot of work!