Release v0.4.3

[stopsack]

Long pending bug-fix release.

risks/NEWS.md

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	# risks 0.4.3
	* One combined user-facing `confint.risks()` function (#7).
	* More intelligible alert about potential data/formula error if no model at all
	can be fit.
	* Always accept missing values in continuous exposures and in covariates in
	`"margstd_boot"` and `"margstd_delta"`.
	* Report confidence limits for a reference category as `0` in `"margstd_boot"`,
	as in `"margstd_delta"`.
	* Add hex logo, thanks to @tgerke.