Adding printf

Development Libraries
6

I was waiting the implementation of printf in core:

But unluckily ive found that it will not be done because Massimo Banzi "dont believe" it should be part of Arduino.

I like both approaches suggested here, but could not make work pYro's library. Instead solution proposed by Okio is simple and straightforward... Just im not sure what is this for:

#if 1
static char _pf_buffer_[_PRINTF_BUFFER_LENGTH_];
#else
extern char _pf_buffer_[_PRINTF_BUFFER_LENGTH_];
#endif