customizable fan shroud

this thing is designed for a J-head full metal type.You can customize it for use with 25x25 mm, 30x30 mm or 35x35 mm fan, and different measures of the hot end.
In new version 2.0, fixes some printing problem, now it´s easy to print and you can use 40x40 mm fans or larger dimensions. it´s very important not use fans that his "y" dimension are longer than total extruder height included the extruder nozzle and heat block heights
In version 2.1, added wall tube to fan screw fasten, the thing is more strong