Now that error string compression is supported it's more important to have
consistent error string formatting (eg all lowercase English words,
consistent contractions). This commit cleans up some of the strings to
make them more consistent.
This adds support for SD cards using the ESP32's built-in hardware SD/MMC
host controller, over either the SDIO bus or SPI. The class is available
as machine.SDCard and using it can be as simple as:
uos.mount(machine.SDCard(), '/sd')
