I have dropped the idea of "formatted stream output".
Basically, what this was doing is "text indentation" (Begin/End operatins increase a number of tabs at beginning of each line) and '\n' -> '\r\n' conversions in Win32.
While nice, it was quite costly. I guess both features are uneeded most of time.
Begin/End was moved to Diag stream, so this is preserved for LOG and friends (the only place were it was really used).
'\r' handling was moved to console output.
Meanwhile, Stream::GetLine was optimized to be about 2x faster (I do not like loosing benchmarks