Support configurable default font and size

Add default_font and default_size options to Document.create, rendered
as w:docDefaults in styles.xml. Defaults to Arial 12pt. Adjust heading
sizes for better visual hierarchy.

Styling based on uutilsynet guidance for accessible documents:
https://www.uutilsynet.no/veiledning/rettleiar-universelt-utforma-word-og-pdf-dokument/1636

lib/notare/xml/styles_xml.rb

@@ -18,9 +18,11 @@ module Notare
         right: "right"
       }.freeze
 
-      def initialize(styles, table_styles = {})
+      def initialize(styles, table_styles = {}, default_font: nil, default_size: nil)
         @styles = styles
         @table_styles = table_styles
+        @default_font = default_font
+        @default_size = default_size
       end
 
       def to_xml
@@ -28,6 +30,8 @@ module Notare
           xml.styles("xmlns:w" => NAMESPACE) do
             xml.parent.namespace = xml.parent.namespace_definitions.find { |ns| ns.prefix == "w" }
 
+            render_doc_defaults(xml) if @default_font || @default_size
+
             @styles.each_value do |style|
               render_style(xml, style)
             end
@@ -44,6 +48,28 @@ module Notare
 
       private
 
+      def render_doc_defaults(xml)
+        xml["w"].docDefaults do
+          xml["w"].rPrDefault do
+            xml["w"].rPr do
+              if @default_font
+                xml["w"].rFonts(
+                  "w:ascii" => @default_font,
+                  "w:hAnsi" => @default_font,
+                  "w:eastAsia" => @default_font,
+                  "w:cs" => @default_font
+                )
+              end
+              if @default_size
+                half_points = (@default_size * 2).to_i
+                xml["w"].sz("w:val" => half_points.to_s)
+                xml["w"].szCs("w:val" => half_points.to_s)
+              end
+            end
+          end
+        end
+      end
+
       def render_style(xml, style)
         style_type = style.paragraph_properties? ? "paragraph" : "character"