1. add uart rx buffer data length API 2. add uart pattern detect event 3. add uart example code 4. modify uart_isr_register 5. modify uart.rst 6. fix parity err event and frame err event.
1. add uart rx buffer data length API 2. add uart pattern detect event 3. add uart example code 4. modify uart_isr_register 5. modify uart.rst 6. fix parity err event and frame err event.