PHP Kilo

A reimplementation of the Kilo tutorial in PHP. Requires PHP 7.4, due to requiring the FFI extension.

Implementation notes:

• The editor prefix has been removed from all the relevant functions, instead they are methods on the Editor class.
• Enums are faked with class constants
• Composer is used for autoloading
• Properties that must be manually updated in the C version (like counts/string length) are implemented with magic methods, so they are essentially calculated on read.
• Generally, if a function exists in PHP, with the same name as the C function, the PHP version will be used.