Do some updates to the serial reference docs

[ganicke]

Update serial reference pages with info about the simulator data log's handling of newlines.

Closes #6649

@martinwork

[martinwork]

Thanks @ganicke! I understand better now. I'd never properly tested sending lots of data without a newline.

When the "Show data" button isn't already showing (e.g. after refreshing the page), the first full buffer or newline from micro:bit triggers the button to appear, but the data is not there when "Show data" is clicked. It seems to be related to switching between simulator and hardware data, with simulator being the default.

I think maybe the buffer limit is 255 rather than 256.

Try this example: https://makecode.microbit.org/_WCDLphDTVHue
Pressing A sends 260 characters. 255 of them appear.

Did you mean to include changes in the code in libs/core/console.ts and sim/state/serial.ts, as well as updating the docs?