Improve the workflow related to the GenCode.php script

The GenCode.php script regenerates all files from source all the time, and this is quite a lengthy process.

This leads to a workflow where GenCode.php is manually executed when needed. So this puts the burden on the developer to notice that a 'source' files has changed during an update, and then take the proper action of manually running the GenCode.php script.

A better workflow is to automatically run the GenCode.php on each update (git pull), for example through the mr script that Tim recommends, and have GenCode.php only regenerate the target file if one of the source files have changed. More or less similar to a typical 'make' workflow.