split jmdict into multiple <4MB files

manifest.json

@@ -18,7 +18,16 @@
     },
 
     "web_accessible_resources": [
-        "dict/JMdict.json",
+        "dict/JMdict1.json",
+        "dict/JMdict2.json",
+        "dict/JMdict3.json",
+        "dict/JMdict4.json",
+        "dict/JMdict5.json",
+        "dict/JMdict6.json",
+        "dict/JMdict7.json",
+        "dict/JMdict8.json",
+        "dict/JMdict9.json",
+        "dict/JMdict10.json",
         "reader.js",
         "reader.html",
         "etc/popupbase.css"