[Rfc-markdown] Releases 1.6.16 to 1.6.20: smaller fixes

[Carsten Bormann <[e-mail]>]

Here is a roll-up of nearly half a year of smaller fixes.

As usual, update with

	gem update kramdown-rfc

(sudo required on some systems).

Grüße, Carsten


## 1.6.20: Ignore target attributes in RFC and I-D bibxml

Since version 1.3.33 [1], kramdown-rfc has had the ability to ignore target attributes in the bibxml obtained for RFCs and I-Ds, allowing xml2rfc to fill in the proper values [1].
For the last couple of years, this needed to be triggered by setting the environment variable KRAMDOWN_NO_TARGETS.
This has been set as the default for Martin Thomson's i-d-template for a long time, and no adverse effects are known.
So with version 1.6.20, KRAMDOWN_NO_TARGETS is now the default; in a pinch use KRAMDOWN_KEEP_TARGETS to revert to previous behavior.

[1]: https://mailarchive.ietf.org/arch/msg/rfc-markdown/8FKkKIMWSsUyy3s89wi3lMvgbUI 2021-02-18

## 1.6.18, 1.6.19

These updates bring the code in line with version 3.2 of the Ruby language, as released 2022-12-25.

## 1.6.17

Kramdown-rfc has fixup code to make some SVG compatible with xml2rfc’s extension restrictions on SVG.
Martin Thomson’s aasvg [2] already conforms to these restrictions, so the fixup code is no longer applied to the output of this tool.

[2]: https://github.com/martinthomson/aasvg ASCII art to SVG

## 1.6.16

The `venue` feature was generating output archive/subscription links even if it didn’t know where they actually had to go.
Fixed.