* Output UART PRINTF on a default Port A9

Improve use of Link-E, making it automatically exit IAP and ARM modes, as well as try very aggressively to reset the processor if it can't attach.

This reverts commit 1c004cba.

 * Fix checksum calculation for escape
 * Add vFlashWrite, vFlashErase and vFlashDone

Closes #159

 * Convert `sandbox` to `template`