OctaveCodePrinter: simplify maintainence of known_functions list

Use a separate list for ones with the same name.  Add more functions.
OctaveCodeGen: clarify it supports both Octave and Matlab

We currently use a subset of Octave to ensure compatibility.
(We should also choose a subset of Matlab to ensure Octave compat,
if that is ever necessary)
OctaveCodePrinter: docstring, comments minor edits
OctaveCodePrinter: "..." no needed before newlines inside matrices