Add basic oo concepts
Complete concepts on oo
Describe how to solve problems in reality
Add randomwalk demo program
Add random walk applications
Reorganize reference list
Plot random-walk distances.
Rename variables

displacement is vector, use drift
Rename variable

Use "displacement" as a fancy way of saying "move".
Add title and labels to plot.
Add multiple trials
Use class variable possible_values

Although the class variable will still be used because
the instance variable does not exist.
Update reference
Define Trial class
Remove Config class
Implement ColdDrunk
Implement EWDrunk
Implement OddField