new directory for logging experiments
Developing experimental sdlog thread
Chasing strange card behavior on existing vs. non-exisiting file.
More experiments with sdlog_thread. Added function to seek to end of file after opening, since there is no open append-mode in FatFS system.
Basic write thread working.

Will detect if card inserted and removed.
Will detect if file exists and create or
open as appropriate.

Currently only writing ascii message for
debugging.