Support unnumbered subsections

[Witiko]

Closes https://github.com/istqborg/istqb_ctal-ta/issues/2.

For example, here is a markdown document that includes an unnumbered subsection:

istqb_product_base/example-document/00-introduction.md

Lines 1 to 21 in 3d26cf9

	# Introduction
	## Purpose of this Syllabus {-}
	This syllabus outlines the scope of the \<module-name\> certification.
	Together with the \<module-code\> body of knowledge the syllabus forms the basis for the International Software Testing Qualification for \<module-name\> at the Advanced Level. The ISTQB® provides this syllabus as follows:
	1. To Member Boards, to translate into their local language and to accredit training providers.
	Member boards may adapt the syllabus to their particular language needs and modify the references to adapt to their local publications.
	1. To certification bodies, to derive examination questions in their local language adapted to the learning objectives for this syllabus.
	1. To training providers, to produce courseware and determine appropriate teaching methods.
	1. To certification candidates, to prepare for the certification exam (either as part of a training course or independently).
	1. To the international software and systems engineering community, to advance the profession of software and systems testing, and as a basis for books and articles.
	## The \<module-name\> Certification
	The ISTQB® \<module-name\> (CTAL-\<module-code\>) certification focuses on organizing and improving quality and testing across multiple teams in an agile organization. It also covers how to approach quality and testing at a strategic level in order to achieve higher business agility in an organization.
	The \<module-code\> qualification is aimed at people who work in organizations that are pursuing agility at scale or business agility and already have a basic understanding of Agile software development and agile testing.
	This includes people in roles such as test manager, head of testing, quality coach, agile test leader, agile test team leader, test analyst, technical test analyst, test automation engineer, quality engineer, quality assurance, member of an agile team, member of a leadership team leading multiple agile teams, IT director, project manager, release train engineer, scrum master, product owner, and management consultant.

Here is the output produced by the template:

@AdamRomanPL: The section is still in the same format (framed box) and still in table of contents, just without the numbering: