Extruder fan holder (angled, parametric)

I needed a fan to blow to extruder radiator and model being printed.

But I wanted slightly different parameters than that of [original Thing](http://www.thingiverse.com/thing:46111). And I wanted fan holder "hands" to have rounded corners.

Original helped me to print mine in good quality, good enough to print [another fan holder](http://www.thingiverse.com/thing:389013) :)