remove 'update' duplications
update assets guide code styling

* 1.9 hash syntax
* proper formatting around one line blocks
* do-end for multiline blocks
Clarified the minute option on DateTime#change
Update guides/source/active_record_basics.md
Update engine application layout file path
Fix typo in guides/source/engines.md
Fix typo in guides/source/engines.md
Fix simple expression
fix reference to ActiveSupport::ProxyObject
Improves documentation about Fragment Caching. [ci skip]

Adds documentation for:
- Aggregate cache keys,
- using an ActiveRecord model as cache key and
- Russian Doll Caching.
fix history
Revert "Improves documentation about Fragment Caching. [ci skip]"

This reverts commit 814c9875ec4cf01e1348d1ab1c9d12eee5a9adac.
Revert "fix history"

This reverts commit dd319600010f4fdc4fac58e5b192bb96fe0d3d7e.
revert to 814c9875ec4cf01e1348d1ab1c9d12eee5a9adac
removes spurious file pushed in cc585c8
Document ActionDispatch::Response#body method
More documentation for ActionDispatch::Response

[ci skip]
Fix formatting error introduced in cc585c8.
Fix typo introduced in 0004ca3a

[ci skip]
clarify awkward sentence re: email testing