Add PHP file caching

[jasny]

We can leverage opcode caching to create a very fast caching method in PHP 7+.

To set the cache use var_export to get the value as PHP code and than write that to a PHP file.
To get the cache simply use include.

Read more about it in this article.

[stevevance]

I really like this idea. I wish that the blog post you linked to @jasny had a bit more code, though, so we could start implementing that concept right away.

[jasny]

Implemented in v3