Expose UART 1

[dnc40085]

Fixes #1907 .

• This PR is for the dev branch rather than for master.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/en/*.

The ESP8266 has two hardware UARTs available, unfortunately the second UART is transmit only due to the fact that the receive pin is shared with one of the flash data lines (SD_D1 to be specific), the UART 1 Tx pin however is unused and available for use.

[codingdaikai]

hi dnc40085,
can you use UART1 TX to output debug log?
I send command uart.setup(1, 115200, 8, uart.PARITY_NONE, uart.STOPBITS_1, 1) to nodemcu,but it still can not output anything.

[dnc40085]

Hello @CAPTAIN888888,
UART 1 can be written to with uart.write(1, "Hello, world\n")