Drop a sqlite_version check because we only support SQLite 3.6.16 or newer.

Drop some comments that document the implementation rather than the interface.
Remove the unused, undocumented SQLite3Adapter#supports_count_distinct?
    
This has returned true since 3cc9b5f1, and is not used internally.
Merge pull request #11921 from Empact/sqlite-3-cleanup

Remove the unused, undocumented SQLite3Adapter#supports_count_distinct?
Move `SchemaCreation` to its own file instead of `AbstractAdapter`.
Fix RailsServer#start content in initialization guide

[ci skip]
[ci skip] Replace #=> with # =>
`remove_column` does not take a type argument. [ci skip]. Closes #12864
[ci skip] Fix curl response output and use strong parameters in update action.
Merge pull request #12865 from JuanitoFatas/layout-and-render

[ci skip] Fix curl response output and use strong parameters in update action
add #no_touching on ActiveRecord models
Correct guide relating MiddlewareStackProxy with Enumerable

[ci skip] Enumerable.instance_methods &
Rails::Configuration::MiddlewareStackProxy.instance_methods # =>
[:as_json]

MiddlewareStackProxy does not share any notable methods with Enumerable.
Revert "`remove_column` does not take a type argument. [ci skip]. Closes #12864"

As of Rails 4.0 `remove_column` is no longer an alias for `remove_columns`.
The type is actually valid and used when issuing a rollback (new `change` method).

This reverts commit 9c9d4948e428a226a19aa92c17fa6ac5833c2fb8.
Remove outdated guide on using rack builder w/o rails middleware

[ci skip]
Ensure that a column added in a test is being removed after all
Fix syntax error in atom_feed example [ci skip]

Builder's #tag! takes either String or Symbol as the first parameter
Merge pull request #12870 from sauliusg/atom-feed-doc-fix

Fix syntax error in atom_feed example [ci skip]
Fix broken Wikipedia link.
move Relation#merge tests into separate file.
tests for merging Relations of different classes.
fix weird Emacs auto indentation. [ci skip]