Re-organize page docs

With verbopse mode (-w), the interpreter shows a warning if
a block is passed to a method which does not use the given block.

Warning on:

* the invoked method is written in C
* the invoked method is not `initialize`
* not invoked with `super`
* the first time on the call-site with the invoked method
  (`obj.foo{}` will be warned once if `foo` is same method)

[Feature #15554]

`Primitive.attr! :use_block` is introduced to declare that primitive
functions (written in C) will use passed block.

For minitest, test needs some tweak, so use
https://github.com/minitest/minitest/commit/ea9caafc0754b1d6236a490d59e624b53209734a
for `test-bundled-gems`.

* Link to packed data doc

* Update pack.rb

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

* Update pack.rb

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

* Update pack.rb

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

* Repair format and links in What's Here for Comparable and Array

* Repair format for What's Here in enum.c

[Feature #18254]

This is useful to avoid repeteadly copying strings when parsing binary formats