Add basic oo concepts
Add gitk option --all

Show all the references
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
Merge branches 'cs' and 'git'