Remove references to deprecared raise_runtime_errors from documentation, which is always enabled now. Ref: https://github.com/rails/sprockets-rails/commit/655b93bffc6f51b96a7cc097f9010942693bfaae and https://github.com/rails/rails/pull/24070 . Fixes #29483 [ci skip] (#29484)

- Replaced MD5 => SHA256 where necessary
- Updated sprockets manifest example

See: https://github.com/rails/sprockets/blob/dd9b3b53c06c602c49057bc4a426c1a446ed7a4a/lib/sprockets.rb#L26

Listening to a few developers today discussing their troubles in understanding how to use the asset pipeline, it turns out that the precompile examples in the guides and assets.rb template have over time become a bit inconsistent.

This PR makes the examples consistent in code style, spacing, and asset names, removes the old 'swfObject.js' example, and in a couple of places wraps lines at 80 characters including in the assets.rb template.

Re-add spaces inside array parentheses.

When referring to Rails, be consistent in usage of capitalized form, unless it is used in context of a command like bin/rails or the rails directory [ci skip]

This config still applies for Rails 4 Apps and we need to mention it, what was needed before. [ci skip]

[ci skip]

Per discussion in #24786.

[ci skip]

`config.assets.raise_runtime_errors` and `config.assets.digest` are enabled
by default in sprockets-rails 3.

s/config\/production/config\/environments\/production/

[ci skip]

for rails/rails#23431

       modified:   guides/source/asset_pipeline.md
* description of asset combination from apps and gems, e.g. jquery-rails
* after @vipulnsward's related change rails/rails#23479
  correction: --skip-sprockets will prevent all of these gems, not just sass-rails and uglifier

       modified:   guides/source/working_with_javascript_in_rails.md
* noted that rails.js requires the asset pipeline

[ci skip]

- sprockets-rails no longer supports customizing cache store after
  rails/sprockets-rails@ecaeb27 using `config.assets.cache_store`.
- Instead we need to configure it using block syntax.
- Fixes #19835.

[ci skip]

Still more to do. Please assist!

JavaScript is spelled with a capital J and S.

It was deprecated in https://github.com/rails/rails/pull/19135.

We're now favoring `public_file_server.headers`.

Should use `public_file_server.enabled` instead.

Clarified that static files will be served from the public directory, where it made sense.

Also removed occurrence of the deprecated `static_cache_control`.