Correctly parse paragraphs with trailing spaces

[Witiko]

Closes #345 and continues https://github.com/danopolan/istqb_latex/pull/77.

Tasks

• Fix the parsing of document example.md from The parser does not parse the full ISTQB example document #345 (comment) by fixing a regression introduced by Allow users to specify logical paragraphs by the number of blank lines between blocks #306.
• Add a regression test for the issue:
  • Add and document support for YAML blocks in testfiles, as described in The parser does not parse the full ISTQB example document #345 (comment).
    • Instead of processing all testfiles with all templates and commands and only masking the results, remove disabled testfiles from batches.
  • Enable special treatment of trailing spaces in tests for ConTeXt MkIV by removing the following lines:
    

    markdown/tests/templates/context-mkiv/verbatim/body.tex.m4

    Lines 7 to 8 in c1af406

    	% Do not preserve trailing spaces in input buffer for parity with other TeX formats.
    	\ctxlua{document.markdown_preserve_trailing_spaces = false}

  • Add a test hard-line-breaks.test, as described in The parser does not parse the full ISTQB example document #345 (comment).
    • Ensure that the test also acts as a regression test for this issue by testing e.g. that trailing spaces at the end of a paragraph do not produce a hard line break.
• Update CHANGES.md.

Nice to haves

• Find all CommonMark examples that test the behavior of trailing tabs and spaces and add them as testfiles that only run with the ConTeXt MkIV format or with the verbatim template.
• Add and document optional fields title, author, and date to YAML blocks. Display these fields in addition to the name of a testfile in test.py.

[Witiko]

• Find all CommonMark examples that test the behavior of trailing tabs and spaces [...]

I created a python file get_examples_with_trailing_tabs_and_spaces.py with the following content:

import json
import sys

for example in json.load(sys.stdin):
    if ' \n' in example['markdown'] or '\t\n' in example['markdown'] or example['markdown'].endswith(' ') or example['markdown'].endswith('\t'):
        print(example['example'])

Then, I ran the following commands, finding 34 CommonMark examples with trailing tabs and spaces:

$ curl -s 'https://spec.commonmark.org/0.30/spec.json' | python3 get_examples_with_trailing_tabs_and_spaces.py
11
54
67
73
79
82
86
89
111
112
117
118
129
193
226
227
240
241
279
282
335
336
337
555
586
633
635
636
638
640
642
645
647
649

$ curl -s 'https://spec.commonmark.org/0.30/spec.json' | python3 get_examples_with_trailing_tabs_and_spaces.py | wc -l
34