ts: clause structure for website-style sources, crash fixes

- documentation sources written for the website start at `###`: the
  generated TS nested clause 4 under 3.3 Abbreviations. The generator
  now adds the missing headings (`4 <NAME> ontology and semantics`,
  `4.1 Introduction and overview`, `4.2 <NAME>`, `4.3 Instantiating
  <NAME>`) and shifts the existing ones (saref-core, saref4syst)
- references are split at the "Informative references" heading of any
  level (saref-core uses h3)
- a project without ETSI work item gets a draft context (TS 103 XXX)
  instead of a TypeError
- annotation properties crashed (`_dt_dd` is a website method); `<img>`
  from markdown crashed; `<div>` without class crashed; empty tables;
  `}}` in code blocks; references with a single heading; symbols with
  markup; History table with more prior versions than template rows
- property characteristics printed empty values; `one of` and `disjoint
  union of` were garbled; data ranges contained HTML spans; data
  property restrictions printed `[?]`; NameError on anonymous inverse
  properties; owl:hasValue false and cardinality 0 were dropped
- HTML comments are no longer inserted as text; `NOTE:\t` spacing
- the generated file is opened with Word only where cmd.exe exists
- README: known limitations from the audit