More Ch-3 fixes

Fixes various sort of typos:

• symbols not in mathmode
• spurious symbols where they shouldn't be
• inconsistent hyphenation
• lines that were mistakenly copy-pasted
• repeated phrases/sentences
• minor grammatical typos
• code typos

Also addresses a couple of code/equation issues:

• use of vtkCallbackCommand vs vtkCommand
• rotation matrix multiply order in the definition of "orientation vector"

Please see commit message bodies for reasoning, especially on the last two items.

@amaclean Thanks!