Added rubocop for style checking; added woodpecker CI config

Gemfile

@@ -10,4 +10,8 @@ gem 'sqlite3', '~> 1.6'
 group :development, :test do
   gem 'rerun'
   gem 'wdm', '>= 0.1.0' if Gem.win_platform?
+
+  # rubocop and extensions for code style
+  gem 'rubocop'
+  gem 'rubocop-sequel'
 end