Instant messages!

Changelog:

- Added IM data and plots.
- Restructured README.md to make plots further up and Technical notes further down.
- A bunch of updated plots for other categories.

 Changes to be committed:
	modified:   README.md
	new file:   plots/chatOverall.png
	modified:   plots/keysOverTime.png
	modified:   plots/polarAll.png
	modified:   plots/polarSplit.png
	modified:   plots/polarSplit2014.png
	modified:   plots/todos.png
	new file:   scripts/IM.R