2.5D Red St.Petersburg Metro Train

This is a 2.5D model inspired by the new red trains in the St.Petersburg Metro.

The model uses 3 or 4 colours, but it is designed to be printable on a single material printer with a bit of manual fiddling.

After slicing, edit your gcode files to insert filament swap commands, for example:

```
; -- filament change to white --
M104 S195 ; set temperature
M600
G1 Z2.400 F7800.000 ; move to next layer (7)
G92 E5 ; reset extrusion distance
```
Make sure that your extrusion distance m