Implement a new module stdio_nimble, which uses nimble
for stdio. The characteristic for stdin is writable and
the characteristic for stdout uses the indicate mechanism
to publish the system's output to a connected device.
Data will be sent out asynchronously via callout functions.
The module can be enabled with "USEMODULE += stdio_nimble"
Co-authored-by: Francisco Molina <femolina@uc.cl>
