src: uart_protocol.c: uart_protocol_handle(): Make logging output more verbose
src: uart_protocol.c: Implement uart_protocol_input_args_hex()

Conflicts:
	TODO
src: uart_protocol.c: uart_protocol_input_args_hex(): Output error log
src: uart_protocol.c: uart_protocol_handle(): Adapt log levels
src: log: Implement logging module with a dedicated output stream

This registers an output stream called logout. It is used internally, as well
as within callback functions to output log messages and makes most of the
dedicated output facilities for callback functions obsolete. This also adapts
already existing callback functions to use to make use of the new facility.
src: log: Add flushing of UART buffer within callback functions

This flushes the buffer whenever a callback function is executed. On top of
that it makes sure that existing callback functions flush the buffer also
every now and then.
src: uart: uart_flush_output(): Add todo item
Merge branch 'feat/streamlog' into feat/log