0.19: erbsland-sphinx-ansi is an optional dependency

[dvzrv]

Hi! 👋

When trying to package 0.19 for Arch Linux, I noticed that erbsland-sphinx-ansi is not only a test requirement, but actually an optional runtime dependency:

sphinxcontrib-programoutput/src/sphinxcontrib/programoutput/__init__.py

Lines 108 to 118 in 50c74a5

	try:
	from erbsland.sphinx.ansi.parser import ANSILiteralBlock
	except ImportError: # pragma: no cover
	logger.warning(
	"programoutput_use_ansi is enabled, but erbsland ANSI support is "
	"not available. Stripping ANSI escape codes instead. Install "
	"'erbsland-sphinx-ansi' and enable 'erbsland.sphinx.ansi' to "
	"render ANSI output."
	)
	stripped_output = _strip_ansi_formatting(output)
	return nodes.literal_block(stripped_output, stripped_output)

From what I can tell, it is not declared as such. However, that would be great to do! :)