docs: Uniform the standards that we should acquire this parsed parame…

[Ryqsky]

Uniform the standards that we should acquire this parsed parameter body through context.query , thus we can avoid confusion and easier to understand the api of docs.

before:
// app/controller/search.js

module.exports = function* (ctx) {
  ctx.body = `search: ${this.query.name}`;
};

after:
// app/controller/search.js

module.exports = function* (ctx) {
  ctx.body = `search: ${ctx.query.name}`;
};

In addition, when we write a Controller by defining a Controller class, it is invalid that we acquire this parsed parameter body through this.query.

// it is invalid.
// app/controller/post.js

module.exports = app => {
  class PostController extends app.Controller {
    * create() {
       // it is invalid. Cannot read property 'name' of undefined
       this.ctx.body = `search: ${this.query.name}`;      
    }
  }
  return PostController;
}

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #1038 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1038   +/-   ##
=======================================
  Coverage   98.96%   98.96%           
=======================================
  Files          28       28           
  Lines         675      675           
=======================================
  Hits          668      668           
  Misses          7        7

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