Created 班级管理系列接口 (markdown)

+####获得所有班级接口
+接口地址：/group
+请求方式：GET
+参数：无
+返回值：
+说明：旧版本无**background**参数
+```json
+[
+  {
+    "learn": "0",
+    "average": "0",
+    "id": 15,
+    "name": "仁者乐山",
+    "createAt": "2015-07-30T11:39:24.929",
+    "updateAt": "2015-07-30T11:39:24.929",
+    "count": 1,
+    "background": "http://image.boxfish.cn/1.jpg"
+  },
+  {
+    "learn": "0",
+    "average": "0",
+    "id": 16,
+    "name": "智者乐水",
+    "createAt": "2015-07-30T14:08:33.436",
+    "updateAt": "2015-07-30T14:08:33.436",
+    "count": 1,
+    "background": "http://image.boxfish.cn/1.jpg"
+  },
+  {
+    "learn": "0",
+    "average": "0",
+    "id": 17,
+    "name": "德玛西亚",
+    "createAt": "2015-07-30T14:09:09.119",
+    "updateAt": "2015-07-30T14:09:09.119",
+    "count": 0,
+    "background": "http://image.boxfish.cn/1.jpg"
+  }
+]
+```
+
+----------------------------------
+
+####更新班级接口
+接口地址：/group
+请求方式：POST
+参数：
+|参数           |是否必须     |说明         |
+|--------------|------------|------------|
+|id            |否          |id为空，是创建班级；id不为空，是更新班级。|
+|name          |是          |班级名称      |
+|summary       |否          |简介         |
+|background    |否          |班级背景图    |
+返回值：
+```json
+{
+  "id": 15,
+  "name": "吼吼吼",
+  "createAt": "2015-07-30T11:39:24.929",
+  "updateAt": "2015-08-06T09:59:52.617",
+  "background": "http://www.boxfish.cn"
+}
+```
+----------------------------------
+####删除班级接口
+接口地址：/group/{group}
+请求方式：DELETE
+参数：{group}为班级id
+接口地址示例：/group/15?access_token=cCBBP9x4vq
+返回值：无
+
+----------------------------------
+####获取班级所有学生接口
+接口地址：/group/{group}
+请求方式：GET
+参数：{group}为班级id
+接口地址示例：/group/15?access_token=cCBBP9x4vq
+返回值：
+```json
+[
+  {
+    "id": 61741,
+    "name": "一口锅",
+    "username": "user150730113647rKlrUqiZ",
+    "nickname": "echo",
+    "realname": "一口锅",
+    "figure_url":    	    "http://q.qlogo.cn/qqapp/101019284/E9C2BA1E2146589CCB69AC8765935819/40",
+    "type": "member",
+    "sum_score": 55
+  },
+  {
+    "id": 61740,
+    "name": "一口大锅",
+    "username": "user150730113647rKlrUqiZ",
+    "nickname": "echo2",
+    "realname": "一口大锅",
+    "figure_url":    	    "http://q.qlogo.cn/qqapp/101019284/E9C2BA1E2146589CCB69AC8765935819/40",
+    "type": "member",
+    "sum_score": 567
+  }
+]
+```