Add \r in retarget

[Joey-Ye]

Serial retarget doesn't output correctly in most of terminal emulator by default, as there is not \r. Output was
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This patch adds \r before \n before sending to UART, which fixes the issue. Tested with linux screen and Windows putty.

[bogdanm]

Sorry to reject this, but changing the data sent by the user is generally not a good idea. Many terminal emulators have an option to automatically append '\r' to the incoming '\n', which should fix the problem.

[errordeveloper]

@Joey-Ye I was originally going to vote 👍 on this as an idea, but then looked at the code and do agree with @bogdanm.

What I think would be a good idea to have is a few debug logger macros, similar to:

    #define debug_logger(msg) \
          printf( "[%s:%d (%s)] %s\r\n", __FILE__, __LINE__, __func__, msg )
    #define debug_format(fmt, ...) \
          printf( "[%s:%d (%s)] "fmt"\r\n", __FILE__, __LINE__, __func__, __VA_ARGS__ )