Updated chapter 6, starting to rewrite chapter 7, and added review environment.
added more "review" problems to chp 6 and 7
Radical rewrites of chapters 7 and 8.  I believe these represent huge improvements. Chapter 7 is completely different. Chapter 8 now starts off with work, then transitions to physical properties, and leave out inertia.  Inertial will be added back in chapter 10.
Update book to chapter 8
Merge branch 'ben' into testmerge

Conflicts:
	06-Derivatives-new.tex
	215-problems.tex
Fix merge problems
Move arclength and area of polar things out of the polar coordinate discussion.
Adjust order of topics in line integrals
Reorder subsections in line integrals yet again.

This time, after a discussion with Ben, I'm putting some space between work/flow/flux and the fundamental theorem of line integrals to give the students time to absorb the concept of work/flow/flux.