Add option to add word count to metadata (#740)

Usage: 
ShowWordCount: true

i18n/es.yaml

@@ -9,6 +9,11 @@
     one : "1 min"
     other: "{{ .Count }} min"
 
+- id: words
+  translation:
+    one : "palabra"
+    other: "{{ .Count }} palabras"
+
 - id: toc
   translation: "Tabla de Contenidos"
 
@@ -25,4 +30,4 @@
   translation: "copiar"
 
 - id: code_copied
-  translation: "¡copiado!"
+  translation: "¡copiado!"