feat: section-type detection, type-specific layouts, and per-section style customisation (v0.7.0)

[Copilot]

The converter applied a single generic layout to all content regardless of structure. This replaces it with a pipeline that auto-detects each ----separated block's type from its ## heading and renders an appropriate layout.

Core pipeline (utils.py)

The old monolithic process_headings/apply_element_styling approach and the 130-entry DEFAULT_STYLE_CONFIG are removed. The new pipeline:

1. handle_images — resolves paths, copies local files (also fixes off-by-one bug stripping static/description/ prefix: 18 → 19 chars)
2. parse_document — splits on ---, then on ## headings, tagging each block with a section type; blocks with no ## inherit the previous type
3. group_sections — merges consecutive same-type blocks (enables multi-block FAQ / Usage)
4. render_section_group — dispatches to a type-specific renderer

Nine section types with dedicated renderers

Type	Layout
overview	intro paragraph + h3 card grid
features	h3 card grid
installation / configuration	centred steps + fenced code blocks
screenshots	responsive gallery (img + blockquote → figcaption)
usage	h3 workflow card grid
known_issues	alert box
faq	Q&A list — one item per --- block
changelog	version-entry cards (h3 = version header)
generic	centred content block

Detection keywords live in SECTION_TYPE_KEYWORDS; the default CSS classes for every rendered element live in DEFAULT_SECTION_STYLES — both exported from the package.

Per-section style customisation

Any key in DEFAULT_SECTION_STYLES is overridable at runtime:

# CLI
md2indexhtml README.md --style-config my_style.json

{
  "overview": { "section_class": "o_section_overview py-5 bg-primary text-white" },
  "faq":      { "question_class": "faq-question h5 font-weight-bold text-primary" }
}

# Python API
convert_md_to_html("README.md", style_config={
    "screenshots": {"grid_class": "row row-cols-1 row-cols-md-3"},
})

HTML document wrapper

Self-contained inline CSS grid + typography reset replaces the prior approach (which referenced Bootstrap classes with no Bootstrap CDN), making output fully standalone and Odoo Apps Store sanitizer-safe.

README

Completely rewritten: section-type detection table, style-key reference, multi-block continuation explanation, CLI/API examples.