TroySQL - Swany: Further integrate PHP for query rewrite.
Add scripts to share/php_scripts
Add variable php_scripts_dir
Add variable php_rewrite_scripts (not yet used)
Extend PHP hook with some built-in function to make the bridge to PHP easier.
  - A function to convert an EXPLAIN FORMAT=JSON explain into the table_info structure the rewriteengine expects
  - A function to return a specific array key from a PHP array (strangely missing in the C++ interface)
  - The actual PHP entry point to the rules system

Work left to do:
Use EXPLAIN to get the JSON for use by the rewriteengine.
Get a plan from the rewriteengine.
Execute the plan in parallel.