ENH Adding read_* support for Google Cloud Storage gs:// URLs
Would be great if pandas were to support reading directly from Google Cloud Storage URLs (gs://), similar to the way it supports AWS s3 URLs (s3://)

Ideally, one could write:
```python
df_csv = pd.read_csv('gs://my-bucket/super-cool-dataset.csv')
df_excel = pd.read_excel('gs://my-bucket/super-cool-dataset.xlsx')

```

I took a quick stab at it in https://github.com/pandas-dev/pandas/commit/4c9196ace8e70f83f81d84d921a73db2581453a4. Let me know if this makes sense and I can add some documentation/tests around it and open a pull request.