Added class simplifiing ledbar output

* also added rainbow.py, which uses this class to create rainbow effect

host_python/rainbow.py

@@ -0,0 +1,33 @@
+#!/usr/bin/python
+# vim:et:sw=4:ts=4:sts=4
+
+import sys
+
+from ledbar import Ledbar
+
+PIXELS = 10
+
+def update(t, i):
+    offset = float(i)/PIXELS
+    time = 0.005*t
+    phi = 6*offset+time
+    phase = int(phi%6)
+    part = phi % 1.0
+    inc = part
+    dec = 1-part
+    if   phase == 0: return (  1, inc,   0)
+    elif phase == 1: return (dec,   1,   0)
+    elif phase == 2: return (  0,   1, inc)
+    elif phase == 3: return (  0, dec,   1)
+    elif phase == 4: return (inc,   0,   1)
+    elif phase == 5: return (  1,   0, dec)
+
+l = Ledbar(PIXELS)
+t = 0
+work = True
+while work:
+    for i in xrange(PIXELS):
+        c = update(t, i)
+        l.set_pixel(i, c[0], c[1], c[2])
+    work = l.update()
+    t += 1