message: Fix manual summary
diff: - [Loops](ch07-02-loops.md)
  - [Matches](ch07-03-matches.md)
  -- [Script Executions](ch08-00-scripts.md)
  +- [Functions](ch08-00-functions)
  -- [Signal Handling](ch09-00-signals.md)
  +- [Script Executions](ch09-00-scripts.md)
  -- [Job Control](ch10-00-jobs.md)
  +- [Signal Handling](ch10-00-signals.md)
  -- [Builtin Commands](ch11-00-builtins.md)
  +- [Job Control](ch11-00-jobs.md)
  -- [Ion by Example](ch12-00-examples.md)
  +- [Builtin Commands](ch12-00-builtins.md)
  - [Command History](ch13-00-history.md)
  