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

vendor/github.com/gomarkdown/markdown/doc.go

@@ -0,0 +1,35 @@
+/*
+Package markdown implements markdown parser and HTML renderer.
+
+It parses markdown into AST format which can be serialized to HTML
+(using html.Renderer) or possibly other formats (using alternate renderers).
+
+Convert markdown to HTML
+
+The simplest way to convert markdown document to HTML
+
+  md := []byte("## markdown document")
+  html := markdown.ToHTML(md, nil, nil)
+
+Customizing parsing and HTML rendering
+
+You can customize parser and HTML renderer:
+
+	import (
+		"github.com/gomarkdown/markdown/parser"
+		"github.com/gomarkdown/markdown/renderer"
+		"github.com/gomarkdown/markdown"
+	)
+	extensions := parser.CommonExtensions | parser.AutoHeadingIDs
+	p := parser.NewWithExensions(extensions)
+
+	htmlFlags := html.CommonFlags | html.HrefTargetBlank
+	opts := html.RendererOptions{Flags: htmlFlags}
+	renderer := html.NewRenderer(opts)
+
+	md := []byte("markdown text")
+	html := markdown.ToHTML(md, p, renderer)
+
+For a cmd-line tool see https://github.com/gomarkdown/mdtohtml
+*/
+package markdown