".. with __dir__ we can restore order in the Universe." - by @fxn

Related to 5b8738c2

While the original sentence is easy to understand, adding the 'to' is
imho a bit more correct.

Sources:
* https://ell.stackexchange.com/q/16964
* https://www.usingenglish.com/forum/threads/127099-It-is-referred-as-or-It-is-referred-to-as

* How to disable scaffolds.scss in generators.md

* Improves workflow customization text in generators.md

- Changed `IN` to `ON` in all note sentences in guides.

With rails/coffee-rails#61 (and #17241), the `.coffee` extension is
favoured over `.js.coffee`. Respectively, with rails/sass-rails#271
`.scss` and `.sass` are favoured over `.css.scss` and `.css.sass`.

Let's update the documentation to reflect that.

[ci skip]

References #18148.

[skip ci]

[ci skip]

Scaffold output: add jbuilder, update timestamp (edge guide!)

Add some file breadcrumb (comment) to help reader find files.

Improve readability by adding some command outputs.

Thanks for great help from @senny.

clarify that the contents of the block is expected to return a string. the previous example executed puts and the initializer got nothing.

also, made it consistent with the single-line example to be more clear as to what's going on

see: https://github.com/blog/1406-namespaced-gists

There's no reason for guides to reference old behaviors. They should
be current as of the versions of Rails that they ship with, and including
older information just clutters thing.

I discussed this change with @fxn and he agrees.

We have three or four different introduction sentences to the guides.
After this commit, we use the same one everywhere.

Talked with @fxn about this. Bullet points should have periods at the ends.

This reverts commit f5b9ed4f.

REASON: Translation work can not be done in the docrails repository

Change the default test locations to avoid confusion around the common
testing terms "unit" and "functional".
Add new rake tasks for the new locations, while maintaining backwards
compatibility with the old rake tasks.

New testing locations are as follows:

    app/models -> test/models (was test/units)
    app/helpers -> test/helpers (was test/units/helpers)
    app/controllers -> test/controllers (was test/functional)
    app/mailers -> test/mailers (was test/functional)