Log warnings and errors to stderr instead of stdout

[jackkoenig]

This has bothered me for a very long time. I'm wondering if this is fine on a minor version or should wait for Chisel 8...

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[seldridge]

This generally makes sense to me. I think it is defensible to send logs to stdout if the tool never uses stdout for anything. However, we should be using stdout for the output FIRRTL or Verilog.

This would make Chisel much closer to a command line generator than the file-based thing that it is now. 👍

[seldridge]

I'd say put everything into errorStream. This would level Info and Debug going to stdout right?

[jackkoenig]

Yeah currently I'm having it send Warn and Error to stderr and the others to stdout, your point is a good one though...