Front page overhaul

[jericson]

Key points:

1. The old version was very 3.0-focused and we are on 4.0.
2. Links to docs should (almost) always go to /master
3. Finding the Guide content is somewhat complicated. Listing it in table of contents form ought to help.

Potential future changes:

1. Explain man1, man3, man5, man7 structure.
2. Link to the Library homepage.
3. Link to the Project, Corporation and Foundation.
4. Maybe include some getting started advice in addition to the guides.