Update markdown parsing library to github.com/gomarkdown/markdown (#944)

vendor/github.com/gomarkdown/markdown/parser/citation.go

@@ -0,0 +1,86 @@
+package parser
+
+import (
+	"bytes"
+
+	"github.com/gomarkdown/markdown/ast"
+)
+
+// citation parses a citation. In its most simple form [@ref], we allow multiple
+// being separated by semicolons and a sub reference inside ala pandoc: [@ref, p. 23].
+// Each citation can have a modifier: !, ? or - wich mean:
+//
+// ! - normative
+// ? - formative
+// - - suppressed
+//
+// The suffix starts after a comma, we strip any whitespace before and after. If the output
+// allows for it, this can be rendered.
+func citation(p *Parser, data []byte, offset int) (int, ast.Node) {
+	// look for the matching closing bracket
+	i := offset + 1
+	for level := 1; level > 0 && i < len(data); i++ {
+		switch {
+		case data[i] == '\n':
+			// no newlines allowed.
+			return 0, nil
+
+		case data[i-1] == '\\':
+			continue
+
+		case data[i] == '[':
+			level++
+
+		case data[i] == ']':
+			level--
+			if level <= 0 {
+				i-- // compensate for extra i++ in for loop
+			}
+		}
+	}
+
+	if i >= len(data) {
+		return 0, nil
+	}
+
+	node := &ast.Citation{}
+
+	citations := bytes.Split(data[1:i], []byte(";"))
+	for _, citation := range citations {
+		var suffix []byte
+		citation = bytes.TrimSpace(citation)
+		j := 0
+		if citation[j] != '@' {
+			// not a citation, drop out entirely.
+			return 0, nil
+		}
+		if c := bytes.Index(citation, []byte(",")); c > 0 {
+			part := citation[:c]
+			suff := citation[c+1:]
+			part = bytes.TrimSpace(part)
+			suff = bytes.TrimSpace(suff)
+
+			citation = part
+			suffix = suff
+		}
+
+		citeType := ast.CitationTypeInformative
+		j = 1
+		switch citation[j] {
+		case '!':
+			citeType = ast.CitationTypeNormative
+			j++
+		case '?':
+			citeType = ast.CitationTypeInformative
+			j++
+		case '-':
+			citeType = ast.CitationTypeSuppressed
+			j++
+		}
+		node.Destination = append(node.Destination, citation[j:])
+		node.Type = append(node.Type, citeType)
+		node.Suffix = append(node.Suffix, suffix)
+	}
+
+	return i + 1, node
+}