This is important if we want to write styled diagnostics to stderr, eg. some
tool outputting results to stdout, but writing styled error messages to stderr.
Previously this module was assuming we are writing only to stdout. Now all
module procs take file handle as first argument. Wrappers assuming stdout are
provided for backwards compatibility.
The new terminal.styledWriteLine(f, args) is provided and documented as
counterpart for unstyled plain writeLine(f, args).
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