(Feature request) Writing of cICP/mDCV/cLLI chunks

[sboukortt]

Currently, those chunks can be read:

image-png/src/common.rs

Lines 688 to 693 in ef61e7e

	/// The coding-independent code points for video signal type identification of the image.
	pub coding_independent_code_points: Option<CodingIndependentCodePoints>,
	/// The mastering display color volume for the image.
	pub mastering_display_color_volume: Option<MasteringDisplayColorVolume>,
	/// The content light information for the image.
	pub content_light_level: Option<ContentLightLevelInfo>,

but not written:

image-png/src/encoder.rs

Lines 593 to 616 in ef61e7e

	// If specified, the sRGB information overrides the source gamma and chromaticities.
	if let Some(srgb) = &info.srgb {
	srgb.encode(&mut self.w)?;
	// gAMA and cHRM are optional, for backwards compatibility
	let srgb_gamma = crate::srgb::substitute_gamma();
	if Some(srgb_gamma) == info.source_gamma {
	srgb_gamma.encode_gama(&mut self.w)?
	}
	let srgb_chromaticities = crate::srgb::substitute_chromaticities();
	if Some(srgb_chromaticities) == info.source_chromaticities {
	srgb_chromaticities.encode(&mut self.w)?;
	}
	} else {
	if let Some(gma) = info.source_gamma {
	gma.encode_gama(&mut self.w)?
	}
	if let Some(chrms) = info.source_chromaticities {
	chrms.encode(&mut self.w)?;
	}
	if let Some(iccp) = &info.icc_profile {
	self.write_iccp_chunk("_", iccp)?
	}
	}

It would be nice to have.

Thanks.