Consider making TreeSequence and TableCollection classes richer by containing NodesTable, EdgeTable, ...

[gregorgorjanc]

Currently we have tc$node_table_add_row() etc. because tc is a TableCollection class with xptr element in it. As such, this resembles C code (so our current implementation looks like a hybrid between C & Python!), while Python code is looks like tc.nodes.add_row() since each table has its own class and associated Python methods. We could mirror such a structure by adding NodeTable, EdgeTable, ... elements to TableCollection, which would be pointers to the tables within the xptr!?

Or we just clearly state that our method/function calls resemble C functions!?

[gregorgorjanc]

Will leave this issue open, but current thinking is that we will not do the full R-Python mapping just now and will make clear in next code push that we really have a hybrid system:

The `RcppTskit R` API combines an `R6` object model inspired by the
`tskit Python` API with operations that map directly to the `tskit C` API.
The `RcppTskit C++` API closely mirrors the `tskit C` API.