Implement R2OAS::Deprecation && Deprecated use of R2OAS.use_object_classes=

[yukihirop]

Summary

Resolve #148

• Implement R2OAS::Deprecation.warn(will_remove)
• Add R2OAS.deprecation.silenced option into Configuration
• Deprecated use of R2OAS.use_object_classes=
• Update docs about R2OAS.deprecation.silenced option

Implemented with considerable reference to ActiveSupport::Deprecation

Work

::R2OAS::Deprecation.will_remove(<<-MSG.squish)
     Using a R2OAS.use_object_classes= in configuration is deprecated and
     will be removed in r2-oas (v0.4.2).
MSG

DEPRECATION WARNING: Using a R2OAS.use_object_classes= in configuration is deprecated and will be removed in r2-oas (v0.4.2). (called from block in reset_config at /Users/fukudayu/RubyProjects/r2-oas/spec/support/helpers/config_helper.rb:32)

Test

./devscript/all_support_ruby.sh rspec

===== Rspec for All Support Ruby Result =====
ruby-2.3.3: 0
ruby-2.4.2: 0
ruby-2.5.8: 0
ruby-2.6.6: 0
ruby-2.7.1: 0
=============================================

Rubocop

$ bundle exec rubocop
Inspecting 209 files
.................................................................................................................................................................................................................

209 files inspected, no offenses detected

[yukihirop]

LGTM