* `std.Buffer.print` is removed; use `buffer.outStream().print`
* `std.fmt.count` returns a `u64`
* `std.Fifo.print` is removed; use `fifo.outStream().print`
* `std.fmt.bufPrint` error is renamed from `BufferTooSmall`
to `NoSpaceLeft` to match `std.os.write`.
* `std.io.FixedBufferStream.getWritten` returns mutable buffer
if the buffer is mutable.
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