The old way mapped each byte of nvm onto a distinct nvs key, but this
allowed storage of only a very small number of bytes out of the
theoretical capacity.
Reworked like this, about half of the nvs capacity can be used for
nvm, so you're guaranteed the ability to store 9kB this way.
* Fix flash writes that don't end on a sector boundary. Fixes#2944
* Fix enum incompatibility with IDF.
* Fix printf output so it goes out debug UART.
* Increase stack size to 8k.
* Fix sleep of less than a tick so it doesn't crash.
