Warnings are written to stdout instead of stderr

[SECtim]

The README says

Errors and warnings are only printed on the console (into the standard error output stream)

However, this is not the case. For example,

rfc-bibtex/rfc_bibtex/rfc_bibtex.py

Lines 127 to 129 in 84bca57

	def _print_no_explicit_version_warnings(self):
	if self._id_drafts_without_version_list:
	print_yellow('WARNING', file=sys.stderr)

seems to print to stderr, but doesn't:

rfc-bibtex/rfc_bibtex/utils.py

Lines 9 to 10 in 84bca57

	def print_yellow(text, end='\n', file=sys.stdout):
	print(f'\u001b[33m\u001b[33m{text}\u001b[0m', end=end)

This is annoying when adding bib entries to a bib file, e.g. rfcbibtex draft-ietf-httpbis-rfc6265bis >> specs.bib, because the warning ends up in the bib file.

[iluxonchik]

Hello,

Thank you for your creating the issue and submitting a merge request. I will review it soon. From a quick check, your observation and code change seems valid. I'll just make sure that that doesn't break anything, and then work it into a release.