Add UTF-8 support

Fix Cortex-M0 Hard Fault

Fix for SparkFun Mbed Apollo3 Core

Improved Teensy SDIO, new features, bug fixes

Add SdFs::format(), improve "const correctness", zip doc

Change SD_FAT_VERSION from string to integer

Timestamp fix, edit src for cplint errors

Add time st

Fix cache bug for FAT16/FAT32

Fix open bug

Add null pointer checks