new post-processing script for the enhanced G29

Hi,
This is the script I use with slic3r. I write it with perl.
This script replaces the custom Gcode parameters [G29XMIN], [G29YMIN], [G29XMAX], [G29YMAX] by their values.
You have first to add a custom gcode in your slicing app like << G29 L[G29XMIN] F[G29YMIN] R[G29XMAX] B[G29YMAX] n4.
With this script :
- only one script file (~80 lines) ;
- no need to compile ; just need a perl interpreter (by default with Linux, on other OS : https://www.perl.org/get.html)
- no min/max values predefined for  x and y coordinates ;
- no need to create a new gcode file ; the user file is updated in place ;
- input and output are streamed ;