Change echo for printf

rationale:
http://unix.stackexchange.com/questions/65803/why-is-printf-better-than-echo

When doing ```make help``` on my setup it printed the newline characters as ```\n``` Like this:
```
- [AUTODETECTED]       Size utility: Basic (not AVR-aware)
-------------------------
\nAvailable targets:\n  make                  - no upload\n  make upload           - upload\n  make clean            - remove all our dependencies\n  make depends          - update dependencies\n  make reset            - reset the Arduino by tickling DTR on the serial port\n  make raw_upload       - upload without first resetting\n  make show_boards      - list all the boards defined in boards.txt\n  make monitor          - connect to the Arduino's serial port\n  make size             - show the size of the compiled output (relative to\n                          resources, if you have a patched avr-size)\n  make disasm           - generate a .lss file in build-cli that contains\n                          disassembly of the compiled file interspersed\n                          with your original source code.\n  make verify_size      - Verify that the size of the final file is less than\n                          the capacity of the micro controller.\n  make eeprom           - upload the eep file\n  make raw_eeprom       - upload the eep file without first resetting\n  make burn_bootloader  - Burn bootloader and/or fuses\n  make help             - show this help\n
```
Changed to printf and it prints properly here.