usart.h: statically define TX buffer like RX buffer. TX buffer size
defined in USART_TX_BUF_SIZE
usart.h: add function usart_reset_tx() to reset TX buffer (same as for
RX bufferI)
usart.c: usart_init() changed to init TX buffer
usart.c: usart_disable() changed to reset TX buffer
usart.c: usart_tx() changed to use TX buffer and manage interrupt TXEIE
usart_f1.c: changed to instantiate TX buffers
usart_private.h: changed interrupt handler to manage TXEIE
edogaldo
stevstrong
Roger Clark