Use symbols instead of strings

ActiveSupport::Concern is used all over Rails
This PR will only create 3 new objects as keys are never recreated and
are not subject to garbage collection.

The strings were being uniquely created and garbage collected. I don't
have any performance numbers but this should be better than all of the
GC.
Improve js written for guides

* Stop using unnecessary global variable
* Use function defined by jQuery for simplicity
* Fix event listner for "more info button" to handle
  event on resize browser
Making the rake file for tests easier to read.

I'm defining a new class which modularizes how the `rake test` tasks are
defined and invoked.
Improved grammar and replaced 'dbs' slang with 'databases'
Add few information about missing steps [ci skip]

Add some deprecations previously note covered such as the confirm
option for the link_to helper or options which aren't needed anymore

Also add a mention about the config.assets.js_compressor option.
cookies are encrypted starting Rails 4
doc for more input tag types
Do not invoke callbacks when delete_all is called

Method `delete_all` should not be invoking callbacks and this
feature was deprecated in Rails 4.0. This is being removed.
`delete_all` will continue to honor the `:dependent` option. However
if `:dependent` value is `:destroy` then the default deletion
strategy for that collection will be applied.

User can also force a deletion strategy by passing parameter to
`delete_all`. For example you can do `@post.comments.delete_all(:nullify)`
Complete a sentence in i18n guide's introduction

Add a list of what will be covered into this guide
Removed params permit step from 5.6 section [ci skip]
Document where `column` param gets utilized in `substitute_at`.
Add missing require

Commit cfa35c55bb38b27af305ad21408e181bc3cd739e removed the
buffered_logger from AS, which required the logger file. Now we need to
add the proper require here.
we don't need to to_s the column
stop exposing the underlying alias datastructure
Remove deprecation messages about protected_attributes and rails-observers
Removed deprecated options for assocations

Deprecated options `delete_sql`, `insert_sql`, `finder_sql` and `counter_sql`
have been deleted.
build an AST rather than slapping strings together
Merge pull request #11222 from neerajdotname/removed-deprecation-for-sql

Removed deprecated options for assocations
only deal with strings internally
make the identity type a singleton to save on object creation