Add "require" packages

[szepeviktor]

• php >= 5.6
• "suggest"? ext-sodium
• phpmailer/phpmailer 6.1.6
• and exclude wp-includes/PHPMailer

Problem: this is only for v5.5.0+

composer require --dev "james-heinrich/getid3:1.9.21"
# Add to bootstrapFiles: vendor/james-heinrich/getid3/getid3/getid3.php
composer require --dev "phpmailer/phpmailer:6.6.0"
composer require --dev "simplepie/simplepie:1.5.8"
composer require --dev "rmccue/requests:1.8.1"

[johnbillion]

I don't think any of these should be included. This library provides non-functional stubs of symbols from WordPress core, there should be no connection between the requirements of WordPress itself and the requirements of this library.