Add support for @kok(alias)

[RussellLuo]

Lengthy

type User interface {
    // @kok(op): POST /users
    // @kok(param): operatorID < in:header,name:Authorization,required:true
    Create(ctx context.Context, operatorID int) (err error)

    // @kok(op): GET /users/{id}
    // @kok(param): operatorID < in:header,name:Authorization,required:true
    Read(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): PUT /users/{id}
    // @kok(param): operatorID < in:header,name:Authorization,required:true
    Update(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): DELETE /users/{id}
    // @kok(param): operatorID < in:header,name:Authorization,required:true
    Delete(ctx context.Context, id, operatorID int) (err error)
}

Simplified

// @kok(alias): auth=`in:header,name:Authorization,required:true`
type User interface {
    // @kok(op): POST /users
    // @kok(param): operatorID < $auth
    Create(ctx context.Context, operatorID int) (err error)

    // @kok(op): GET /users/{id}
    // @kok(param): operatorID < $auth
    Read(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): PUT /users/{id}
    // @kok(param): operatorID < $auth
    Update(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): DELETE /users/{id}
    // @kok(param): operatorID < $auth
    Delete(ctx context.Context, id, operatorID int) (err error)
}

Or

// @kok(alias): opID=`operatorID < in:header,name:Authorization,required:true`
type User interface {
    // @kok(op): POST /users
    // @kok(param): $opID
    Create(ctx context.Context, operatorID int) (err error)

    // @kok(op): GET /users/{id}
    // @kok(param): $opID
    Read(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): PUT /users/{id}
    // @kok(param): $opID
    Update(ctx context.Context, id, operatorID int) (err error)

    // @kok(op): DELETE /users/{id}
    // @kok(param): $opID
    Delete(ctx context.Context, id, operatorID int) (err error)
}