documents optimization

[dead-horse]

now we received some feedback and realized lots of features are undocumented.

• 404 configuration 路由未匹配，如何统一返回404页面 #352 @dead-horse
• session 怎么将session保存到redis、mongo、mysql中，是不是要写egg-session-redis、egg-session-mongo、...插件 #353 @dead-horse
• pm2 egg编写入口文件，pm2启动。 #345 @shaoshuai0102 doc: add pm2 faq #370
• tutorials index docs: add tutorials index & fix async #359 @atian25
• split plugin docs to plugin and plugin-development
• add egg-static document
• multiple processes introduction @dead-horse

[popomore]

We can add an index page for tutorials, replacing mysql now. It contains a list for some normal case like db access, session, react...

[atian25]

build-in middleware also need docs

[shaoshuai0102]

#370

[atian25]

• how to define special loader rule
• deployment

[popomore]

document for app.beforeClose

[atian25]

• env document missing default description

[atian25]

document about github workflow

[atian25]

• split plugin docs to plugin and plugin-development
• add egg-static document

[popomore]

https://github.com/eggjs/doctools

[popomore]

• generate build-in plugin document
• test document