Plot velocity as color: hue for direction and saturation for speed

Usage: [hi,hcw]=hsvel([x],[y],u,v,[maxspeed],[options])
Given a gridded velocity field specified by two-dimensional arrays "u" and "v", hsvel plots the velocity with color, representing direction with hue and speed with saturation, returning the image handle in "hi". A ColorWheel is also plotted to serve as a key; its handle is returned in "hcw". If the corresponding coordinates are given as vectors "x" and "y" they are used as well. Optionally, specify the speed for full saturation with "maxspeed". You can also provide a list of options (e.g. 'DisplayName','myname') to be passed to image.m when plotting.