Rippled-APIs improvements

The following improvements to the rippled-APIs page:
- Add "Try it!" links to relevant API methods
- Add JSON-RPC examples for almost all methods
- Pre-rendered the content for better rendering performance and SEO

The following improvements apply to all the API references:
- Flatdoc sidebar no longer overlaps footer at certain window widths
- Sidebar no longer shrinks to accommodate footer when not scrolled to bottom