- support standard lib <string> by default, default enable Arduino_STD_PRINTF that allows printf() and _rtl_printf() simultaneously
- include -DArduino_STD_PRINTF as extra-flag
- modify the define sequence of min() max() in wiring_constants.h to remove compilation error
- ensures downward compatibility
- remove extra printf() debug message in ard_socket.c

Verification:
Verified on Arduino IDE1&2 with Ameba D series: AMB21/22/23/25/26 BW16/BW16TypeC AWCU488 and u-blox NORA-W30

- support standard min/max function from \arm-none-eabi\include\c++\6.5.0\bits\stl_algobase.h
- support Arduino defined min/max function defined in wiring_constants.h