ToC is now aware of toc-title

### New feature

Elements that creates heading (i.e.	h1,h2,h3 by default) will now get the text given on `data-toc-title` if it's available instead of the text of the element to create the navigation element.
Fixing indentation back
Merge pull request #43 from Belelros/feature/41-data-toc-title

ToC is now aware of toc-title