Update link docs, browser-version
Update link docs, browser-version

* Added notes for each link to indicate ordering and if the user can
change the link or order.
* Dropped previous and next links from browser-version
* Added release-day and retirement-day attributes to browser-version
* Changed current=true to status=current, with other values for
  status ("retired", "beta", "future")
* Added section on sources of version information

jwhitlock/web-platform-compat,mdn/browsercompat,mdn/browsercompat,jwhitlock/web-platform-compat,renoirb/browsercompat,mdn/browsercompat,renoirb/browsercompat,renoirb/browsercompat,jwhitlock/web-platform-compat