Ender 3 maintanance g-codes

I leave here 3 usefull gcodes that I use basically everytime I print something on my ender 3. Each one is for:

- (32m)bed_cleaning_sheet: prints a very thin layer that lets you get off all the small printing residue that it's imposible to get off with a scraper. The "(32m)" stands for the time it takes to print.
- Bed_calibration_test: moves the nozzle in all 4 corners and the center in order to make the paper calibration test. It also repeats itself again after the calibration so you can check twice if it's ok.
- Change_filament: purges out the old spool, let's you insert the new one and purges the old one.

This is a compilation of g-codes I've found all over thingiverse, so if you made some of them feel free to say so. Also the "ERROR" file is just to bypass the upload requierment of thingiverse so just ignore it.