* documentation：modify and fix 3 points

1）默认脚手架生成的工程「egg-init egg-init egg-example --type=sim...

closes https://github.com/eggjs/egg/issues/185

remove egg-rest and egg-cors and static enable by default

mv to https://github.com/eggjs/examples/pull/3

* feat: support app.config.proxy to identify app is behind a proxy

* test: fix cookie test

Closes #227
Ref #211

close egg#130

* feat: add a dns cache httpclient

Usage:

```js
// enable on urllib config
exports.urlli...

Closes eggjs/egg#118

- broadcast is changed, it will send to all process
- send is changed, it won't emit message

...

consoleLevel on unittest is WARN, so it should be print,
but egg disable console after app read...

closes https://github.com/eggjs/egg/issues/123

it can be override with custom function

Closes eggjs/egg#36

* feat: support background task on ctx

```js
ctx.runAtBackground(function* (ctx) {
// asy...

logger should close stream when app close

can improve 6x on node 6.x
see https://gist.github.com/fengmk2/d7d0091a5eeae8ce0c9580f31e748371