Only cache template digests if config.cache_template_loading

since ActionView::Resolver.caching is set to the same value as config.cache_template_loading
only cache template digests if config.cache_template_loading is not falsy
fixes issues #10752 and #10791
Moved "`mod_expires` to be enabled" to new line.

- Right now the comment was not rendering properly.
  # The Expires* directives requires the Apache module
  `mod_expires` to be
  # enabled.
- After this change -
  # The Expires* directives requires the Apache module
  # `mod_expires` to be enabled.
Removing merge conflict remnants in the guides.
Document ability to run a single test.
Add Finder API changes to upgrading guide [skip ci]
Warning on doc for assets under lib|vendor not precompiling
Merge pull request #12015 from vipulnsward/add_dynamic_finders_to_upgrade

Add Finder API changes to upgrading guide [ci skip]
Soften wording about knowing other devs.

Many people don't, so point them to a place where they can meet
some.
Flesh out feedback portion of contributing guide.

I don't know of anyone that hangs out in #rails-contrib, and we should
also let people know that feedback can take some time.
Add note about features vs. bugs.

Sometimes people ask what makes a feature and what makes a bug, so
let's clarify that so we can show it to people later.
Updating README.md [ci skip]

Updating the global Rails README following work by @strzalek et al which extracted Action View to a separate gem, and also some other improvements.

Summary of changes:

* Reordered the paragraphs from View-Model-Controller to Model-Controller-View, based on how (IMHO) most people think about the structure and hierarchy of the framework and their code in it.
* Added references to ActionView's README in the _View_ paragraph
* Reworded the _Controller_ paragraph to briefly mentioned routing as handled by Action Dispatch, and that both Action Dispatch and Action Controller work together to form the request-handling Action Pack
* Removed paragraph saying Action Pack is coupled with Action View, as this is no longer the case
* Added brief references to Action Mailer and Active Support, since they are both major Rails components. Briefly mentioned in the _View_ paragraph that Action View is often used to generate the body of the email, in addition to the other typical of using to build a response body.
Merge pull request #11986 from fedesoria/patch-3

Warning on doc for assets under lib|vendor not precompiling
Add config to method calls in fixtures.

Allows you to change your configuration for calls to
`table_name_prefix`, `table_name_suffix`, and `pluralize_table_names`.
The default configuration is still ActiveRecord::Base, but you are now
able to change the configuration easily.
Remove whiny_nils config from the rails guides

This option was removed from master.

[ci skip]
Merge pull request #12032 from carolinemota/fixdoc

Remove whiny_nils config from the rails guides [ci skip]
Merge pull request #12034 from wangjohn/fixtures_config_changes

Add config to method calls in fixtures.
Perf: fields in pg gem causes an allocation, cache it
Perf: avoid array allocation where not needed
Merge pull request #12037 from SamSaffron/mem_alloc

Performance: Reduce memory allocations in Active Record
Perf: memoize serialized column list and time zone column list