add todo percentage in item list

browser/lib/getTodoState.js

@@ -0,0 +1,25 @@
+export function getTodoState (content) {
+  let splitted = content.split('\n')
+  let numberOfTodo = 0
+  let numberOfCompletedTodo = 0
+
+  splitted.forEach((line) => {
+    let trimmedLine = line.trim()
+    if (trimmedLine.match(/^[\+\-\*] \[\s|x\] ./)) {
+      numberOfTodo++
+    }
+    if (trimmedLine.match(/^[\+\-\*] \[x\] ./)) {
+      numberOfCompletedTodo++
+    }
+  })
+
+  return {
+    total: numberOfTodo,
+    completed: numberOfCompletedTodo
+  }
+}
+
+export function getTodoPercentageOfCompleted (content) {
+  const state = getTodoState(content)
+  return Math.floor(state.completed / state.total * 100)
+}