updated AS:Callbacks doc for terminator option in define_callbacks method
The change is commited at ba552764344bc0a3c25b8576ec11f127ceaa16da
Adding find_by in guide to methods that trigger after_find
unified the param names across all callbacks manipulation methods
_ Rename the define_callbacks params to `names`
  - in order to match the naming conventions for `get_callbacks` and `set_callbacks` at https://github.com/rails/rails/blob/master/activesupport/lib/active_support/callbacks.rb#L736-743
  - `define_callbacks` just register names(events), not define the real callback functions.
- Rename the `reset_callbacks` params
Using preferred find_by syntax in guides
Merge pull request #11204 from Gawyn/find_by-triggers-after_find

Adding find_by in guide to methods that trigger after_find
Merge pull request #11205 from Gawyn/using-preferred-find_by-syntax-in-guides

Using preferred find_by syntax in guides
Merge pull request #11195 from yangchenyun/update_doc_for_define_callbacks

updated AS:Callbacks docs, variable namings
Allowing multiple rails applications in the same ruby instance.

This change provides the ability to create a new application with a
configuration which can be specified.
s/plugin_new/plugin

There are historical reasons that the `plugin` command was `plugin_new`, now those are no longer applicable, we should remove the naming edge case from the project. This PR is based off of comments from #11176

ATP Railties
Remove redundant escapes from xml serialization test
Merge pull request #10099 from wangjohn/railties_each_with_config_2nd_attempt

Created way of cloning a Rails::Application instance
Further clean-up of ActiveSupport::Callbacks

In #11195 I noticed a trailing comma in the docs, but I decided to
further clean it up.

What I have done:

* Clean up the trailing comma in the docs and some extra whitespace
  lines.
* Used `Array#extract` options to factor the repetitive pattern of
  `args.last.is_a(Hash) ? ...`
* Renamed the local var `config` to `options` in `define_callbacks`, as
  `options` seems to be the de facto name for the options objects.
* Renamed the local var `l` to `line` in `define_callback` (maybe it
  meant `lambda` in the context) as single `l` may look like `1` in some
  fonts.
Merge pull request #11211 from gsamokovarov/trailing-comma

Further clean-up of ActiveSupport::Callbacks
Merge pull request #11207 from vipulnsward/remove_escapes

Remove redundant escapes from xml serialization test
Using ActiveSupport::Concern instead of plain regular Ruby hooks in railties/lib/rails/generators/migration.rb file
Removed deprecated method default_scopes?
Removed deprecated method scoped
Merge pull request #11203 from schneems/schneems/plugin_new-plugin

s/plugin_new/plugin
Merge pull request #11212 from neerajdotname/default_scopes_q_deprecated

Removed deprecated default_scopes?
Merge pull request #11213 from neerajdotname/scoped-deprecated

Removed deprecated scoped method

Conflicts:
	activerecord/CHANGELOG.md