Log Message:
ruby-kramdown: Update to 2.3.0

Changelog:
kramdown 2.3.0 released

Although this is a minor version bump there is one breaking change:
Parsing of XML processing instructions was removed because they
are invalid for HTML5 documents.

This change should only affect a negligible amount of existing
kramdown documents since XML processing instructions were never
something a normal user would use.

Additionally, CVE-2020-14001 is addressed to avoid problems when
using the {::options /} extension together with the ‘template’
option. This means updating is highly recommended!

Changes

    2 major changes:

	New option ‘forbidden_inline_options’ to restrict the
	options allowed with the {::options /} extension. This also
	addresses the security issue described in CVE-2020-14001.

	Parsing of XML processing instructions is not done anymore
	for kramdown documents because they are invalid for HTML5
	(fixes issue #660 by Samuel Williams)

    1 minor change:

	Several internal changes with respect to memory usage and
	performance (PRs #654, #655, #665 by Ashwin Maroli)

    2 bug fixes:

	Extend allowed characters in IDs set with headers to all
	characters allowed by XML (fixes #658 by Samuel Williams)

	Fix thread safety issue by moving global state into an
	instance variable (fixes #663 by Samuel Williams)

    1 other change:

	Documentation fixes and updates (issue #662 by Samuel
	Williams, PR #656 by Noah Doersing)