Dropped PHP 5 support and improved code

Please welcome our new co-maintainer Patrick @phh who has made this release possible!

Changelog:

• (internal) Switched to minimum PHP version of 7.2 and added tools to fix formatting #64, #66, #67, #69
• (refactoring) Language file path without base path #63
• (refactoring) Rely on lang_path() and resource_path('lang') for getting the language file path #62