Reorganize "Cache Stores" sections [ci-skip]

This makes "Connection Pool Options" a subsection of "Configuration",
instead of a subsection of "ActiveSupport::Cache::Store".  This also
makes "Custom Cache Stores" its own section after all of the built-in
stores, instead of a subsection of "ActiveSupport::Cache::Store".

Author: jonathanhefner

guides/source/caching_with_rails.md

@@ -373,21 +373,6 @@ Alternatively, you can set `ActionController::Base.cache_store` outside of a con
 
 You can access the cache by calling `Rails.cache`.
 
-### `ActiveSupport::Cache::Store`
-
-[`ActiveSupport::Cache::Store`][] provides the foundation for interacting with the cache in Rails. This is an abstract class, and you cannot use it on its own. Instead, you must use a concrete implementation of the class tied to a storage engine. Rails ships with several implementations, documented below.
-
-The main API methods are [`read`][ActiveSupport::Cache::Store#read], [`write`][ActiveSupport::Cache::Store#write], [`delete`][ActiveSupport::Cache::Store#delete], [`exist?`][ActiveSupport::Cache::Store#exist?], and [`fetch`][ActiveSupport::Cache::Store#fetch].
-
-Options passed to the cache store's constructor will be treated as default options for the appropriate API methods.
-
-[`ActiveSupport::Cache::Store`]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html
-[ActiveSupport::Cache::Store#delete]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-delete
-[ActiveSupport::Cache::Store#exist?]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-exist-3F
-[ActiveSupport::Cache::Store#fetch]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-fetch
-[ActiveSupport::Cache::Store#read]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-read
-[ActiveSupport::Cache::Store#write]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-write
-
 #### Connection Pool Options
 
 By default, [`:mem_cache_store`](#activesupport-cache-memcachestore) and
@@ -411,18 +396,20 @@ config.cache_store = :mem_cache_store, "cache.example.com", pool: { size: 32, ti
 
 * `:timeout` - This option sets the number of seconds to wait for a connection (defaults to 5). If no connection is available within the timeout, a `Timeout::Error` will be raised.
 
-#### Custom Cache Stores
+### `ActiveSupport::Cache::Store`
 
-You can create your own custom cache store by simply extending
-`ActiveSupport::Cache::Store` and implementing the appropriate methods. This way,
-you can swap in any number of caching technologies into your Rails application.
+[`ActiveSupport::Cache::Store`][] provides the foundation for interacting with the cache in Rails. This is an abstract class, and you cannot use it on its own. Instead, you must use a concrete implementation of the class tied to a storage engine. Rails ships with several implementations, documented below.
 
-To use a custom cache store, simply set the cache store to a new instance of your
-custom class.
+The main API methods are [`read`][ActiveSupport::Cache::Store#read], [`write`][ActiveSupport::Cache::Store#write], [`delete`][ActiveSupport::Cache::Store#delete], [`exist?`][ActiveSupport::Cache::Store#exist?], and [`fetch`][ActiveSupport::Cache::Store#fetch].
 
-```ruby
-config.cache_store = MyCacheStore.new
-```
+Options passed to the cache store's constructor will be treated as default options for the appropriate API methods.
+
+[`ActiveSupport::Cache::Store`]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html
+[ActiveSupport::Cache::Store#delete]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-delete
+[ActiveSupport::Cache::Store#exist?]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-exist-3F
+[ActiveSupport::Cache::Store#fetch]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-fetch
+[ActiveSupport::Cache::Store#read]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-read
+[ActiveSupport::Cache::Store#write]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/Store.html#method-i-write
 
 ### `ActiveSupport::Cache::MemoryStore`
 
@@ -577,6 +564,19 @@ config.cache_store = :null_store
 
 [`ActiveSupport::Cache::NullStore`]: https://api.rubyonrails.org/classes/ActiveSupport/Cache/NullStore.html
 
+### Custom Cache Stores
+
+You can create your own custom cache store by simply extending
+`ActiveSupport::Cache::Store` and implementing the appropriate methods. This way,
+you can swap in any number of caching technologies into your Rails application.
+
+To use a custom cache store, simply set the cache store to a new instance of your
+custom class.
+
+```ruby
+config.cache_store = MyCacheStore.new
+```
+
 Cache Keys
 ----------