Update README.rdoc [ci skip]

Highlighted code
Update commands.rb content in initialization guide

[ci skip]
Add section for command_tasks in initialization guide

[ci skip]
Change syntax format for example returned values

According to our guideline, we leave 1 space between `#` and `=>`, so we
want `# =>` instead of `#=>`.

Thanks to @fxn for the suggestion.

[ci skip]
Fix RailsServer#start content in initialization guide

[ci skip]
[ci skip] Replace #=> with # =>
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.
Remove outdated guide on using rack builder w/o rails middleware

[ci skip]
Fix broken Wikipedia link.
Update action_controller_overview.md [ci skip]

Code style adherence
The option is called encode_big_decimal_as_string [ci-skip]
added test cases to find notes in a file with .builder extension
Merge pull request #12921 from kuldeepaggarwal/documentation-updation

[ci skip]updated documentation: added sass and less extensions
Drop unused param `should_be_quoted` to `PostgreSQLColumn#array_to_string`
Merge pull request #12928 from vipulnsward/drop_unused_param

Drop unused param `should_be_quoted` to `PostgreSQLColumn#array_to_string`
Properly require database tasks so we have access to the raised constant

Fix travis failures.
Add description for db:create and db:drop test tasks in AR

This will help identify these tasks exists, since they are easier to
setup things for running all AR tests.
Address test_merging_where_relations failure by adding `order("posts.id")`
Merge pull request #12929 from yahonda/test_merging_where_relations_add_order

Address test_merging_where_relations failure by adding order
Do not count query for all_constraints and all_tab_cols in Oracle