Improve `<thread>` functions reference

[Rageking8]

• Add leading sentence and backticks
• Simplify and improve links
• Add basic example for get_id
• Update syntax (see microsoft/STL/stl/inc/thread L200-L225):
  • Add missing this_thread:: for those in the std::this_thread namespace
  • Remove inline in sleep_for, and format it
  • Remove void sleep_until(const xtime *Abs_time); since it no longer exists
• Update metadata