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.