turtle can now have multiple fading pixel 'fires'

 - colors are stored as HSL, which allows scaling lightness
 - tail wags when you press the shell button
 - pressing amber adds fires
 - pressing green removes fires
 - pressing blue gives you new colors

each of the fires is a pixel that starts black, the pulses to the desired
color, then back to black.  taking between 2.5 and 5 seconds total.