'ins' command should accept 'g2' objects

[goessner]

It is implemented by

    ins(arg) {
        return typeof arg === 'function' ? (arg(this) || this)                   // no further processing by handler ...
             : typeof arg === 'object'   ? ( this.commands.push({a:arg}), this ) // no explicit command name .. !
             : this;
    },

and

    async exe(commands) {
        for (let cmd of commands) {
            if (cmd.c && this[cmd.c]) {         // explicit command name .. !
                const rx = this[cmd.c](cmd.a);
                if (rx && rx instanceof Promise) {
                    await rx;
                }
            } else if (cmd.a) {                 // should be from 'ins' command
                if (cmd.a.commands)                // cmd.a is a `g2` object, so directly execute its commands array.
                    this.exe(cmd.a.commands);
                if (cmd.a.g2)                      // cmd.a is an object offering a `g2` method, so call it and execute its returned commands array.
                    this.exe(cmd.a.g2().commands);
            }
        }
    },

Please add and test.