Add variadic print(String...) function

Just found this:
http://stackoverflow.com/questions/10044449/a-function-with-variable-number-of-arguments-with-known-types-the-c11-way

Add this to Print.h:

``` cpp
template
size_t println(const String &head, TailType&&... tail)
{
size_t r = 0;
r+=println(head);
r+=println((tail)...);
return r;
}
```

Now you can do stuff like this:
Serial.println("Hey", "this", "is", "a", "Test");

Every word is printed in a new line. You can also add this for Serial.print (without newline).
Maybe this can be optimized to only print the last input with a new line. An overload with two arguments is needed here I guess.

Not sure if its perfect c++, but this would give us the option to print infinite strings at once.
Maybe one can generalize this even more to also print numbers (without formating of course, just DEC).

It takes a lot of flash though. But maybe someone can optimize this further? (Now that we also have c++11 with the merged PR)

Any comments on that?

**Edit:** Maybe this is also relevant. This uses **the same size as if there was no template**.
It can also handle numbers (without format).
https://msdn.microsoft.com/en-us/library/dn439779.aspx

``` cpp
template
inline size_t println(const First& first, const Rest&... rest) {
size_t r = 0;
r+=println(first);
r+=println(rest...); // recursive call using pack expansion syntax
return r;
}
```

Another example (ln now only adds a new line at the end):

``` cpp
template
inline size_t println2(const First& first) {
return println(first);
}

template
inline size_t println2(const First& first, const Rest&... rest) {
size_t r = 0;
r+=print(first);
r+=println2(rest...); // recursive call using pack expansion syntax
return r;
}
```