Added getFaces() method 

We have a face detection now for simplecv-js.

to use it in console you can use the following code.
<code>

display = new Display(".livePreview")
size = display.resolution()
console.log size
Camera.beginStream((i)=>
  i = i.resize size[0], size[1]
  dl = i.addDrawingLayer()
  dl.noFill()
  comp = i.getFaces()
  for face in comp
    dl.rect(face.x, face.y, face.width, face.height)
  i.show display
)
<code/>