Implement a insert_multiple()

[vetsin]

We have update_multiple and delete_multiple which take advantage of the batch api -- no reason to not do the same with insert.

I imagine something like:

gr = client.GlideRecord('some_table')

gr.initialize()
gr.name = 'first'

gr.initialize()
gr.name = 'second'

gr.insert_multiple() # or maybe even just gr.insert()

We may want to 'iterate' the record to make it more obvious?