make printTo stop if it the stream can not take more bytes

[me-no-dev]

also returns the actual bytes written

[bblanchon]

This increases the code size by 152 bytes, which represents about 4% of the size of the encoding library.
The feature doesn't justify such an increase.
Moreover, there isn't any test.

@me-no-dev, I know the problem you're trying to solve and I know that this is the wrong solution.

One way to solve your issue is to implement coroutine in a Print implementation.
Unfortunately this is currently impossible on the ESP8266 since setjmp() and longjmp() are not yet supported.
I still haven't found any other solution that doesn't ruin the code size and complexity.

I'm sorry but I'm not going to accept this pull request.