Dual fan mount for Printrbot Simple Metal

After publishing [my experiment about how fans and fan shrouds affect overhang success and appearance](http://www.desiquintans.com/coolingtests), I became curious about whether using dual fans would improve my results. I couldn't find anyone who had made a frame to hold two print-cooling fans onto a Printrbot Simple Metal, so I designed my own.

[I have experimentally demonstrated](http://www.desiquintans.com/coolingtests2) that using two fans instead of one improves the printing success and s