Add "streaming" syntax support to Print class

I wrote a couple of lines of helper code to allow for easy printing. If anyone is interested, I could incorporate it in `Stream.h` and open a pull request.

Usage:

```cpp
int a {9};
int b {10};
Serial << "You have " << a << " out of " << b << " retries left.\n";
// Prints: "You have 9 out of 10 retries left."
Serial << makePair(1.2, 4) << ' ' << makePair(12, BIN) << '\n';
// Prints: "1.2000 1100"
```

Start by reading Stream.h and the Print class, then compare the requested << usage examples with the existing printing API. Done means the shown string, integer, character, and makePair examples are supported and produce the documented output.

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