Bugfix/issue 742 arm ch2

#### Summary:

minor changes to example scripts and data for Chapter 2

#### Intended Effect:

all example code in script 2.3_CI.R runs as is.

#### How to Verify:

from R, source script 2.3_CI.R

#### Side Effects:

none.

#### Documentation:

README file for Chapter 2 documents data file "plots.dat"

#### Reviewer Suggestions:

none