Fix Print for long long

Printing huge integer numbers did not work; this patch repairs this.
Additional, in Print() was uint8_t buf[34]; which was bigger than
nessesary.

Testsketch (did not work before):

#include <climits>

void setup(){
Serial1.begin(115200);
Serial1.println();
Serial1.println();
Serial1.println(LONG_MIN);
Serial1.println(LONG_MAX);
Serial1.println(ULONG_MAX);
Serial1.println(LLONG_MIN);
Serial1.println(LLONG_MAX);
Serial1.println(ULLONG_MAX);
}

void loop(){
}