We must become more dynamic, introducing the QueryLoaderQueryLoader

Hello,

I found this project quite delightful indeed. It has some quite remarkable features. However, one limiting factor when running this in a distributed manner, is that there is no central place to store the queries in a consistent and reliable way. The obvious solution is to use an SQL database for storing the queries.

Introducing, the QueryLoaderQueryLoader. It loads its own queries from a different query loader, then executes those queries on a query that you can define. This allows queries to be swapped in an atomic manner across the entire system, simply by updating a row in the table. It also allows for rapid iteration and on-the-fly adjustments without having to re-deploy code or config files.

You must pass it a QueryLoader from which it will load the queries for fetching the requested queries. This query loader has a strictly defined interface of two queries, that have the following signatures:

* **has-query-meta-query** this is the query that returns the query for checking if a query of a certain name exists. The query stored there takes one `:name` parameter as an input, and must return a row with a `count` field, indicating whether the name exists.

* **get-query-meta-query** this is the query that returns the query for fetching a query by name. The query stored there takes one `:name` parameter as input and must return a row with a `query` field, containing the query that the user requested by name.

For basic usage, just pass `$pdo` and `$loader` arguments to the constructor:

    $pdo = new PDO(...);
    $metaQueryLoader = new FilesystemQueryLoader('meta-queries');
    $queryLoader = new QueryLoaderQueryLoader($pdo, $metaQueryLoader);

    $nqm = NQM($pdo, $queryLoader);
    $nqm->...();

However, it becomes more interesting when you pass the QueryLoaderQueryLoader to itself:

    $queryLoader = new QueryLoaderQueryLoader($pdo);
    $queryLoader->setLoader($queryLoader);

This will put the query loader into a special mode where the CPU goes round and computes the maximum stack size of the PHP interpreter.

PS: I didn't really test this code, but I'm pretty sure it works. I wrote something similar once and it worked too. Either way, really excited about this node query manager!