adjusted various details:

- changed floppiness implementation
- changed default flopiness
- made heaband rounder
- added hingetest

headband.scad

@@ -5,7 +5,7 @@ RAKE_CHAMFER=0.5;
 
 module partial_ring(part, radius, thickness, height) {
   rotate(180-180*part, [0, 0, 1])
-    rotate_extrude(angle=360*part)
+    rotate_extrude(angle=360*part, $fn = 128)
       translate([radius, 0]){
         polygon(points = [[thickness/2,height/2-0.5],
                           [thickness/2-0.5,height/2],