multiline fix for Octave
multiline fix for Octave

Use ">> " for first line of block, but then use ".. " for
subsequent lines.  This makes multiline code work.  For example

@example
@group
A = [1 2 3;
     4 5 6;
     7 8 9]
@result{} A =
   1   2   3
   4   5   6
   7   8   9
@end group
@end example

catch22/octave-doctest