True 16 bit transfer, and new loop friendly 16 bit transfer

[drmcnelson]

This replaces the transfer16() with a true 16 bit transfer, adds a new loop friendly 16 bit transfer, and rename the old transfer16() as two bytes to transfer16_asbytes()

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[per1234]

Thanks for taking the time to submit a pull request @drmcnelson.

Arduino has a strict policy that we can only accept pull requests after the contributor has signed the contributor license agreement. Since you have stated in #363 that you refuse to sign the agreement, we can not accept this pull request.

[drmcnelson]

In fact I did sign the CLA, I filled in the form, ticked the box and clicked the button.

Your software after that asked for access to my private data. When a bot asks for access to private data, that is where I draw the line, as any normal person should.

I plan to keep the fork up, or at least the patched SPI support with the functioning and improved 16 bit transfers. It seems there are people who want it.

Or, you could incorporate into the main tree yourself, you certainly have my permission to do that. Just let me know if you do.