Updated to use absolute imports

I used to add .\code to the path, which was an absurd hack.
Now all code is imported with import code.foo.

code/ekf_internal.py

@@ -16,7 +16,7 @@ for more information.
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
-import book_plots as bp
+import code.book_plots as bp
 import filterpy.kalman as kf
 from math import radians, sin, cos, sqrt, exp
 import matplotlib.pyplot as plt