Documentation layout rework

Our pages are too long-running, and the content is poorly organised. We should prepare some mockups and revamp the general layout. Some ideas to consider:
- One page per component, rather than one page per category of components.
- Sub-navigation inside each page, to separate examples from class reference and JSDoc reference.
- Better usage of anchors to save history between components.
- Better layout for displaying examples, to avoid exceeding screen width in mobile.