add separate driver for W25N01GV triggered via HAL_LOGGING_DATAFLASH_DRIVER
move flash_test() into AP_Logger_Block.
cleanup use of 4k sector commands to account for chips that only have block commands
be really careful to catch aborted erases
take care to protect shared structures in io thread
if flash corruption is detected try and recover whole files
overwrite format in erase to make sure erase happens
output useful messages at critical times
a block is 64k a sector is 4k, rename internal variables appropriately
cope with log wrapping when sending log listings over mavlink