Extract links and point them at kspro.com/perma/*

[3v0k4]

Instead of hardcoding links in the gem, we can use permalinks that perform a 302 redirect, which we can update without requiring anybody to update the gem (and can be tracked if needed).

Example:

• knapsackpro.com/perma/ruby/encryption -> 302 -> https://docs.knapsackpro.com/ruby/encryption/

Inspiration

• Elm (compiler errors contain links)
  • https://elm-lang.org/0.19.1/bad-recursion -> https://github.com/elm/compiler/blob/master/hints/bad-recursion.md
• Rust (compiler errors contain codes that can be explained)
  • https://github.com/rust-lang/rust/blob/5efa4c0555ef2879d9cb5d9e0d247ee767e2fa10/compiler/rustc_error_codes/src/error_codes/E0001.md
  • rustc --explain E0001
• eslint (linter errors contain links)
  • https://eslint.org/play/
  • https://github.com/eslint/eslint/blob/3ae0574fc78c4a2b406625e4792cb2859cb9bcb1/lib/rules/no-constructor-return.js

[ArturT]

It looks good.

I added comments for the PR on the API side that could impact the links here.