Code refactoring: renamed time macros.
Code refactoring: replaced all types by those defined in stdint.h.

All type definitions are now explicit in regard with the size of the
variable.

Fixed indents in the code.
Code refactoring: removed dead and useless code.
Board config: modified UART configuration.

Modified the peripheral configuration to switch off data reception
(which is unused). Activated Tx interrupts.

Modified code indentation.
main: The code now stores data in the data frame used for downlink.
main: Implemented interrupt-based downlink transmission.

The code uses a circular buffer to send data through the UART link.
Transmission is interrupt-based to avoid wasting time waiting for the
completion of the transmission of the full array.