CassResult missing functions

[Lorak-mmk]

Both _count and cass_result_column_type and cass_result_column_name should be easy (if Rust driver has support, but it probably has).
Not sure about cass_result_column_data_type and cass_result_paging_state_token.

• cass_result_row_count
• cass_result_column_count
• cass_result_column_name
• cass_result_column_type
• cass_result_column_data_type
• cass_result_first_row
• cass_result_paging_state_token

API docs:
https://docs.datastax.com/en/developer/cpp-driver/2.16/api/struct.CassResult/

[Lorak-mmk]

cass_result_column_type and cass_result_column_data_type require #18

[muzarski]

This will be closed when https://github.com/scylladb/cpp-rust-driver/pull/136 is merged.