Pystow

- Unify interface for download functions (normal, google, and S3)
- Add hash checking functionality to download() and download_from_google() (https://github.com/cthoyt/pystow/pull/7; thanks mberr )

Fix bug in google download - now uses consistent session

Add google drive downloader. Use like:

python
import pystow
path = pystow.ensure_from_google('test', name='wk3l15k.zip', file_id='1AsPPU4ka1Rc9u-XYMGWtvV65hF3egi0z')

add handling for dtype in `pystow.get_config()`

Deal with file clean up if the file was never created