docs/library/machine.UART.rst: Specify optional txbuf and rxbuf args.
docs/library/machine.UART.rst: Specify optional txbuf and rxbuf args.

If a port would like to expose the configuration of transmit and/or receive
buffers then it can use these arguments.

henriknelson/micropython,selste/micropython,kerneltask/micropython,bvernoux/micropython,pfalcon/micropython,henriknelson/micropython,pozetroninc/micropython,trezor/micropython,pozetroninc/micropython,bvernoux/micropython,tobbad/micropython,pozetroninc/micropython,adafruit/circuitpython,pramasoul/micropython,pozetroninc/micropython,henriknelson/micropython,pfalcon/micropython,trezor/micropython,selste/micropython,pramasoul/micropython,MrSurly/micropython,adafruit/circuitpython,kerneltask/micropython,kerneltask/micropython,MrSurly/micropython,pfalcon/micropython,kerneltask/micropython,adafruit/circuitpython,trezor/micropython,MrSurly/micropython,pramasoul/micropython,selste/micropython,selste/micropython,tobbad/micropython,adafruit/circuitpython,MrSurly/micropython,bvernoux/micropython,tobbad/micropython,bvernoux/micropython,pfalcon/micropython,pozetroninc/micropython,trezor/micropython,henriknelson/micropython,adafruit/circuitpython,MrSurly/micropython,henriknelson/micropython,tobbad/micropython,kerneltask/micropython,pfalcon/micropython,tobbad/micropython,pramasoul/micropython,bvernoux/micropython,adafruit/circuitpython,selste/micropython,trezor/micropython,pramasoul/micropython