Add links to sr.ht repos and add an image in the README file

Make sure to send pending keys

even if the FP is flood by the CPU: hijack the started transmission
(just after receiving a SoT (0x66) datagram).

Possibly fix the 'reset FP while running' case

Revert to soft reset on RST irq

Reduce the sleep time of the send_pending_key thread to 1ms

to get a chance of sending a keycode when the CPU flood the FP with DSP
messages (e.g. after the last 'Last-N' value).

Clean several compilation warnings

Fix SHIFT and code cleanup

Make USBSerial work -- at last

It needs the revision 4587080d of mbed-os to work (i.e. mbed-os>6.15.0)

Simplify a bit the rst logic and make a bit more robust

Stop splashscreen after 5s

Formatting

Remove dead custom board definition

Write a README file

Do not go to the next line if the char to display does not fit

Small fixes in main

- toggle the shift indicator when the key is pressed while already on
- attempt to fix the restart-while-shuting-down bug

Attempt to normalize the 19x27 font

make all "main" characters 15px wide.

foldme

Refactor the flag display system

make it stateful

Reorganize the display + improvements for dimmed flags

- the whole upper zone is now dediacated to the main character line
- make sure eash flag has a dedicated non-overlaping area
- improve support for dimmed flags (not yet properly functionning since this
  dimm state is actually stateful, so some major refactorings are needed to
  properly handle this).

Add support for 0x08 and 0x09 command codes (display a flag dimm/bright)