fix: issues with multi-page and minor refactor

Thanks for the cool component!

This PR includes the following:

* Fixes issues when your steps don't start at 1. This happens in the multi-page example right now. Try to click the navigation to see the errors.
* Solidifies the logic behind the anchor navigation
* Refactors unnecessary double loop
* Also triggers complete callback when you try to go back on the first item. This is useful so you can have a callback called when you need to know when to redirect the user to a previous page. This could be changed to a different event/callback name. Open to discussion.
* Fixes broken HTML in the samples
* Minor code style fixes
* Minor sample modification

Any questions or suggestions, feel free to discuss!

Best regards