Add support for GNU Octave 4.0

[genemiller]

Summary

1. Readme.md: Added configuration and code change instructions to run Matlab demo code in GNU Octave 4.0.
2. Dataset.m and randin.m: code changes for GNU Octave 4.0 (described in Readme.md)

Notes

• All changes were tested on GNU Octave 4.0 on Windows 10.
• The latest binary distribution for MAC OS (GNU Octave 3.8.2) does not support classdef. To make the code work in this environment, change Dataset.m to a struct. I.e. remove the classdef statement, remove the properties section, and move each one of the methods into a separate file.
• I don't have a Matlab environment needed to test the Dataset.m superclass change ('matlab.mixin.copyable' -> 'handle'). I.e., I couldn't verify whether this change actually works in Matlab, or see if it degrades performance, results in too much memory usage, or has other negative side effects.
• The Readme.md instaructions are probably sufficient if you decide not to accept the code changes.
• If you accept the code chnages, then you may remove the redundant instructions from Readme.md.