Fetch schema (Not Fully Documented Issue)

[Daniel-Boll]

Todo

I still need to document this issue

https://rust-driver.docs.scylladb.com/stable/schema/schema.html

[Matozinho]

The get_cluster_data function has been implemented in ScyllaSession. From the ClusterData module, the only function that has been migrated so far is get_keyspace_info, which provides access to data similar to that found in this Rust driver documentation.

A few functions from ClusterData could still be useful to migrate, such as get_endpoints and get_nodes_info.

[Daniel-Boll]

As the PR #33 doesn't fully implement this issue it should either not close it or another issue describing the remaining stuff be created.