Support reading query results with multiple pages and other dataset helper methods

[pirsquare]

• Supports reading query results with multiple pages for get_query_rows
• Make get_query_results public
• Add missing get_dataset method
• Add check_dataset

[tylertreat]

We might want to add a note in the docstring of this method that it will append each page of results, which is potentially a very expensive call. If users want to manually page through results, they can use get_query_results. I think in general, we should probably make the docstrings of get_query_rows and get_query_results more detailed since it might not be obvious what the difference between the two is.

[tylertreat]

Looks good. Just one note about making the docstrings a bit more clear.

[tylertreat]

Thanks!