Parametric standard hinge

# Parametric standard hinge

* open position with no swag (unless configured)
* printed in place
* non-removable captured pin
* pin is along y axis
* reinforced knuckles extruded from leaf for improved strength
* all values can be modified and have reasonable defaults

Current revision of this on git: https://gitlab.com/stgnet/parametric

# PARAMETERS:

knuckles = number of knuckles, defaults to 7, if even pin will be exposed and unsupported on one end
note: if knuckles is set to 2, the two leafs can be separated

hinge_length = y dimension of entire hinge starting at y=0, defaults to 8mm per kuckle

hinge_width = x dimension of entire hinge with center on x=0, defaults to 40mm

knuckle_diameter = diameter of knuckles around pin, defaults to 1/5 of hinge_width

pin_center_height = distance from bottom of hinge to center of pin, defaults to half of knuckle_diameter