Adds "flog" and some changes inspired by it.

Flog measures the complexity of the code, and this commit adds the flog gem
and a rake task for running it.

The commit also changes lib/scaler because some of its flog scores were a bit
high...

Before:

 ratdog:ruby mike$ rake flog
    80.6: flog total
    13.4: flog/method average

    29.1: Scaler#initialize                lib/scaler.rb:16
    27.3: Mandelbrot::simple               lib/mandelbrot.rb:9

After:

 ratdog:ruby mike$ rake flog
    67.4: flog total
     7.5: flog/method average

    27.3: Mandelbrot::simple               lib/mandelbrot.rb:9
    12.4: Scaler#calculate_scale           lib/scaler.rb:38
     9.8: Scaler#perform_scaling           lib/scaler.rb:46

(I don't care that much about Mandelbrot::simple because it's a transcription
of some known code.)