MMC problems on (some?) SD cards

Commands on the SD Card do not work correctly when sent immediately after a response or after , without clocking the card by sending 0xFF through SPI. I was getting error status responses from the card for perfectly good commands. [This Stack Overflow answer](https://stackoverflow.com/a/2375234/7455223) helped me solve this after spending hours on the problem. It seems this is only a problem with some SD cards (at least that's what the Stack Overflow answer suggests): I imagine it was tested on one that didn't suffer from this clocking requirement.

I was using a 16gb SanDisk Ultra SD Card (mounted on an [Adalogger Featherwing](https://www.adafruit.com/product/2922)).

For now I will leave my dirty debugging code that did manage to fix the problem for me, and will update when I have time to make it into something cleaner.