PR Summary

Update some of the introductory topics, cleanup comments and refactor a couple of the koans mainly in the introductions section.

Changes

• Refactor AboutArrays commentary and a couple of the koans
• Refactor AboutAssertions introductory text
• Refactor AboutBinary introductory comments and koans
• Refactor AboutBooleans introductory comments
• Refactor AboutNumbers commentary and add a koan or two
• Refactor AboutStrings commentary and adjust a couple of koans slightly.

Checklist

• Pull Request has a meaningful title.
• Summarised changes.
• Pull Request is ready to merge & is not WIP.
• Added tests / only testable interactively.
  • Make sure you add a new test if old tests do not effectively test the code changed.
• Added documentation / opened issue to track adding documentation at a later date.