{%- macro ref(slug, abs=False) -%}
{% set path, sep, fragment = slug.strip("/").partition("#") %}
{% set ns = namespace(found=false, page=None) %}
{% set pathpart = "/{}".format(path) %}
{%- for page in site.pages if page.url.endswith(pathpart) or (page.source and page.source.path.endswith(pathpart)) -%}
    {%- if ns.found -%}
        {{- raise("cannot uniquely resolve ref to {} ({} and {})".format(slug, ns.page.relurl, page.relurl)) -}}
    {%- endif -%}

    {% set ns.found = true %}
    {% set ns.page = page %}
{%- endfor -%}
{%- if not ns.found -%}
    {{- raise("ref to {} not found".format(slug)) -}}
{%- endif -%}
{% if abs %}{{ ns.page.url }}{% else %}{{ ns.page.relurl }}{% endif %}{{ sep }}{{ fragment }}
{%- endmacro -%}

{%- macro figure(src, class=None, alt="") -%}
<figure{%- if class %} class="{{ class }}"{% endif %}>
    <img src="{{ src }}"{%- if alt %} alt="{{ alt }}"{% endif %} />
</figure>
{%- endmacro -%}