OctaveCodePrinter: cleanup, ternary operator, comments

I learned the ternary operator: neat!
OctaveCodePrinter: fix "1./x" and similar.

This means we stop using Str._print_mul, so changes there are not needed.
Revert "StrPrinter: add kwarg to _print_Pow and _print_Mul to override symbol"

This reverts commit c6c7c61349c2d93777679b51f6209ec1cbe15435.
Revert "StrPrinter: allow subclasses to change the symbol used for exponents"

This reverts commit 3027c9cae2c01464bbd84bfe01eeafb6d4185853.
Revert "StrPrinter: add kwarg to _print_Pow and _print_Mul to override symbol"

This reverts commit c6c7c61349c2d93777679b51f6209ec1cbe15435.

Conflicts:
	sympy/printing/str.py