Add C bindings and Go wrapper for ReadMany APIs

Once we have the ReadMany APIs from #36 in and validated, we should update the C bindings to expose them. This will require a little bit of thought about how best to represent things, but should be pretty straightforward.

Then, we need to update the `azcosmoscx` package in this repo to wrap those APIs in safe Go code for use by the Go SDK.

Start by reviewing issue #36 and the existing C bindings for the ReadMany APIs. Then inspect the `azcosmoscx` package; the work is complete when the C bindings expose ReadMany and the package provides safe Go wrappers for use by the Go SDK.

Written by the indexing model from the issue text.