I was reviewing some docs and found a few issues.
1. Fixed some spelling mistakes.
2. Re-formatted some paragraphs.
3. Changed some potentially loaded language.
4. Fixed some grammar issues.
5. Tried to consistently use syntax-highlighting.
6. Fixed post-period spacing.
7. Fixed some formatting issues and inconsistency.
8. All "notes" are either proper notes or re-written.
Default MaxStale to 10 years and add a counter at `consul.dns.stale_queries` that tracks when an agent serves a query that's stale by at least 5 seconds. Previously, MaxStale defaulted to 5 seconds and DNS would become unavailable after a short period of time with no leader. This new default allows DNS requests to still be served in the event of a long outage.
Fixes#2460.
