Shortest distance between two line segments

Computes the shortest distance between two line segments given start and end points for each. Adapts the algorithm found on Dan Sunday's website (http://softsurfer.com/Archive/algorithm_0106/algorithm_0106.htm#dist3D_Segment_to_Segment
).
Usage: Input the start and end x,y,z coordinates for two line segments.
p1, p2 are [x,y,z] coordinates of first line segment and p3,p4 are for
second line segment.

Output: scalar minimum distance between the two segments.

Example:
P1 = [0 0 0]; P2 = [1 0 0];
P3 = [0 1 0]; P4 = [1 1 0];
dist = DistBetween2Segment(P1, P2, P3, P4)
dist =

1