correct and enhance ch3 applied questions

relative error in 8aii) was referring to independent var
12b) and 12c) needs +0 to fit through origin
Added a new example to 12c) to illustrate other situations this fit
could be generated
13a) chas is a factor variable, so translated it to one. This affects
whether it is significant
15b) no need to ignore the independent var, this is done automatically
Chapter 7: Exercise 6, 9, 10 and 11
Generic proof that R^2 is equal to squared correlation
Figures for chapter 7 exercises

Change-Id: Ic73509675ce2d28279158895acd13a36f722569b
Complete Chapter 6: Exercises 10, 11
Merge pull request #33 from asadoughi/ch6_10-11

Completed Chapter 6: Exercises 10, 11
Merge pull request #32 from ksamdev/ch3/ex7

Generic proof that R^2 is equal to squared correlation
Housekeeping for ch3e7
Merge pull request #20 from kungfujam/master

correct and enhance ch3 applied questions
Correct Chapter 3: 15a post-merge of PR #20
Completed Chapter 7: Exercises 1 - 5
6(b) debug
6(b) k=8 gives minimum cut
Merge pull request #30 from sjuvekar/master

Chapter 7: Exercise 6, 9, 10 and 11
Completed Chapter 7: Exercise 12
Completed Chapter 7: Exercises 7 and 8
Chapter 8 applied exercises
Chapter 9 applied

Change-Id: I63d3d91f9e6529a438291e2c0e20049d21c9ec9d
Completed Chapter 8: Exercise 1
Updated README.md