Setup gem and search strings in ruby files

[f19ps]

Tasks done:

• Make the initial set-up.
• Add Rubocop and Reek.
• Search strings in ruby files.
• Log the output in the console.
• Handle many Ruby versions on CircleCI

Things to keep in mind:

1) The main executable is located in bin/i18n_linter. When the gem is installed in any project and it runs i18n_linter this file will be executed. 2) In this PR I'm searching any string in ruby files and logging the output in the console. 3) It's possible to indicate a file pattern where searches the strings or just leave this by default.