Add function getConnection() to Application for database.

[zoujiaqing]

You can use it like code:

module app.controller.IndexController;

import hunt.framework;

class IndexController : Controller
{

    mixin MakeController;

    @Action
    string index()
    {
        auto connection = app().database().getConnection();

        auto stmt = conn.createStatement();
        stmt.prepare("SELECT * FROM user WHERE username = :username AND age = :age LIMIT 10");
        stmt.setParameter("username", "zoujiaqing");
        stmt.setParameter("age", 18);

        foreach(row; stmt.query())
        {
            writeln(row["username"]);
        }

        return "";
    }
}