Wholesale changes to connect chapters together.

I made a lot of changes so that each chapter makes clear that
they are all implementing the same basic bayesian algorithm.

This required a lot of editting, and it doesn't make sense to
try to do that atomically, hence this huge check in.

I made a lot of edits, and haven't copy editted anything. i'm
sure I introduced a lot of problems and discontinuities.

code/DogSimulation.py

@@ -0,0 +1,44 @@
+# -*- coding: utf-8 -*-
+"""
+Created on Sun May 11 13:21:39 2014
+
+@author: rlabbe
+"""
+
+from __future__ import print_function, division
+
+from numpy.random import randn
+import math
+
+class DogSimulation(object):
+
+    def __init__(self, x0=0, velocity=1,
+                 measurement_variance=0.0, process_variance=0.0):
+        """ x0 - initial position
+            velocity - (+=right, -=left)
+            measurement_variance - variance in measurement m^2
+            process_variance - variance in process (m/s)^2
+        """
+        self.x = x0
+        self.velocity = velocity
+        self.measurement_noise = math.sqrt(measurement_variance)
+        self.process_noise = math.sqrt(process_variance)
+
+
+    def move(self, dt=1.0):
+        '''Compute new position of the dog assuming `dt` seconds have
+        passed since the last update.'''
+        # compute new position based on velocity. Add in some
+        # process noise
+        velocity = self.velocity + randn() * self.process_noise
+        self.x += velocity * dt
+
+    def sense_position(self):
+        # simulate measuring the position with noise
+        measurement = self.x + randn() * self.measurement_noise
+        return measurement
+
+    def move_and_sense(self, dt=1.0):
+        self.move(dt)
+
+        return self.sense_position()