Add InsertBatch

[saromanov]

Hi! I just added simple extension to the API is Insert Batch method. So, Insert allows to add single object and Insert Batch is for add multiple objects.
Part of the code:

obj1 := &TestObject{
    ID:  "my-cool-thing",
    Foo: "abc",
}
obj2 := &TestObject{
    ID:  "my-other-cool-thing",
    Foo: "xyz",
}
obj3 := &TestObject{
    ID:  "yet-another-cool-thing",
    Foo: "xyb",
}

err := txn.InsertBatch("main", obj1, obj2, obj3)
if err != nil {
    panic(err)
}

[armon]

There is no real advantage over just calling Insert multiple times, so for the sake of API simplicity I'm closing this.