Markdown
- Switch <strong> wrapper from `__` to `**` so it doesn't clash
  with literal underscore runs (Word fill-in fields).
- Replace mammoth's blanket text escape with a context-aware one:
  `*` `_` `(` `)` `{` `}` are never escaped; `#` `+` `-` `.` only
  when at line start in a position that would actually parse as
  syntax; `[` `]` only when forming the inline-link pattern
  `[text](url)`; `!` only before such a pattern. `\` and backtick
  remain always escaped.
- Drop HTML <a id> anchors from Markdown output (kept in HTML).

Numbering
- Read <w:start> from <w:lvl> and forward it as `start` on <ol>,
  so a Word document that splits "1., 2., 3." into separate
  single-item ordered lists no longer renders as three "1."s in
  a row. The MarkdownWriter honours `<ol start="N">` and
  continues from there.