Improve the libraries page

Description

The libraries page can be improved.

Tasks

• Introduction text: page goals: how it can help developers.
• New columns for the libraries table:
  • Maintenance status, with:
    • A defined maintenance criteria. Example: library had a repository update no older than a year. But is this the best criteria?
  • Stability level: prototype, stable etc.
  • Whether it's officially maintained by Tor, or if it's maintained by the community.
• Collect feedback/input on tor-dev mailing list.

Time estimation

• Complexity: very small (0.5 day)
• Uncertainty: low (x1.1)
• Reference (adapted)