Add paging to query.py

[MichaelCurrin]

Also update usage doc.

See code such as

repo_page_info = repositories['pageInfo']
        if repo_page_info['hasNextPage']:
            variables['cursor'] = repo_page_info['endCursor']
        else:
            break

Test against queries with and without pageInfo in their output.
If cursor/after is provided in variables (or some flag to prevent paging esp on first page), then do not do automatic paging.

Consider how the output looks (printing data as you go or joining data in a larger file and then writing).

Also see if this is even needed. The paging is handled specifically in other Python scripts, where the case is not general.