Extract TableCollection interface #307
Description
The TreeSequence class could stand to access elements of the
TableCollection API.
Similar to how tskit-python works, it would be nice to say ts.tables().foo(...).
To do this, we'd take the public interface of a table collection
and extract it to a separate struct.
The current table collection would have this new type as a deref
target and a tree sequence would own an instance of this type,
giving an API:
pub fn table(&self) -> &TableCollectionInterface {
&self.tables_interface
}