feat: Add soungbook example

- Add songbook to demo
- Add macro for song
- Add style module

source/style/demo.scss

@@ -11,5 +11,6 @@
 // -----------------------------------------------------------------------------
 @import "modules/card/card_module";
 @import "modules/portal/portal_module";
+@import "modules/songbook/songbook_module";
 @import "modules/demo/demo_module";
 // @import "modules/YOUR-MODULE/YOUR-FILES";

source/style/modules/songbook/_songbook_module.scss

@@ -0,0 +1,20 @@
+.songbook_song {
+	pre {
+		@extend .pre_code
+	}
+
+	header {
+		h2 {
+			margin-bottom: $space_basic;
+		}
+
+		h6 {
+			color: $color_brightest;
+		}
+
+		h2+h6 {
+			margin-top: 0;
+			margin-bottom: $space_small;
+		}
+	}
+}