Update Guide for coefficient reordering.

[aaustin141]

Now that chebfun/chebfun#991 has been dealt with, the Guide needs some updating to reflect the new ordering of the coefficients. Right off the bat, I can see that sections 1.6 and 4.2 require some revision, but there may be more places.

[aaustin141]

After merging #8, the Guide no longer crashes with the new reordering, but there may still be some places which require revision to the text itself.