add regexp docs

Author: jameszhan

02-ruby-basics/02.03-strings.ipynb

@@ -597,7 +597,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "`s.split(pattern, [limit])`以给定的pattern为分隔符对s进行分割。"
+    "`s.split(pattern[, limit])`以给定的pattern为分隔符对s进行分割。"
    ]
   },
   {

02-ruby-basics/02.04-symbols.ipynb

@@ -7,6 +7,88 @@
     "# 符号"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## 创建 `Symbol`\n",
+    "\n",
+    "### 典型构造\n",
+    "\n",
+    "典型地，**Ruby**中可以在字符串之前加上 `:` 生成 `Symbol`。"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       ":hello"
+      ]
+     },
+     "execution_count": 2,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    ":hello"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       ":\"hello world\""
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    ":'hello world'"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### 特殊构造\n",
+    "\n",
+    "* %s: 不支持 `interpolation` 和 `escaping`\n",
+    "* 你可以使用任何典型的分割字符，例如`%s{...}`, `%s(...)`, `%s|...|`, `%s?...?`, `%s-....-`, `%s/.../`, etc"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       ":\"this is \\\"hello\\\" 'world'\""
+      ]
+     },
+     "execution_count": 4,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "s = %s(this is \"hello\" 'world')\n",
+    "s"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {