Additional Info for MEX File Distribution

[colbysparks]

I've left a comment on this PR, but was directed to create an issue because the topic might be worthy of broader discussion. Here is the comment and response for anyone who is interested.

I think the new MEX best practices guide is very helpful, but it would be great if it included some additional information on limitations and implications of using MEX in ML toolboxes, such as:

• The stability of C, C++ and Fortran MEX interface and matrix APIs between different MATLAB versions.
• Best practices on how to package MEX files while are compiled for different incompatible versions of MATLAB.
• A warning that you cannot upload a toolbox to the MATLAB Central File Exchange if it includes compiled MEX files.

[rpurser47]

@colbysparks I'm still working to put this info together, but we're going to release the MEX guidance in a couple of weeks without this info. I don't want to delay that while I get definitive answers to these questions.