Recursion Update for php-json-schema

[loneregister]

Amazon's Schema system necessitated an update to allow recursion in the RefResolver object beyond 200. This code updates the system to allow an option to be submitted via option->maxNestLevel if recursion greater than 200 is needed. (or less).

Example: `$options = new \Swaggest\JsonSchema\Context();

$options->maxNestLevel = 500;

$schema = Schema::import($data, $options);`

My first attempt to provide a fix / better feature - be gentle.

[loneregister]

Updated issues to address P0, P1 and P2 commentary.

[loneregister]

Is there anything else I need to do here, to have this reviewed, and accepted.