datastore_create can't upload a json records file

datastore_create() method accepts a `records` parameter with a list of dictionaries. It will be converted to json by the api..

All types in the dictionary must be jsonable. A datatime value in the dict will issue a validation error.

To fix it I must convert my pandas dataframe to json string, have it loaded back to a python dictionary and then pass it as a parameter to the method that will convert it again to json.

It is very inefficient, specially for large datasets.

I'd like to be able to directly pass a json string to the datastore_create() or datastore_upsert() to have it sent to CKAN