Add Flag Deprecation Page + Codespell config

[dereknola]

Addresses: https://github.com/k3s-io/docs/issues/127

• Adds https://github.com/k3s-io/k3s/blob/master/docs/adrs/deprecating-and-removing-flags.md as a Reference page, with cleanup language and example.
• Removes references to old dqlite releases.
• Removes stub Reference page, which was Out of Date
• Rework codespell to contain all config in single file, not just ignore words