v0.2. "Ubik"

This is a substantial upgrade in terms of content and code quality.

Substantial updates.

• Adding prediction and machine learning classes for Chapters 13-18 of the Data Analysis textbook
• Adding a lecture on spatial data visualization (yes, map!)
• Adding a lecture on matplotlib vs plotnine libraries for graphs

Minor updates

• Restructure some files -- making them simpler, clearer (hopefully)
• add missing README files