* corret type clause
* add tests, changes in create_json_string
* create json-string now gives back None
* revert changes
* fix panda sql export
* add SQL test
* fixed None type export for csv and sql.gz
* move None parsing to json io
* alter regex
* revert changes
* only replace None with empty str when necessary
* fixed deserialze_df for python 3.7
* add more tesets
* fix case where gz was ignored
* hand voer gz explicitly
* replace nan by None in non-Obs columns
* moved warning to csv export, mroe tests
* only values able to be nan are put in np.isnan()
* added python float for warning
* feat: Added serialization of list of Obs in pandas.to_sql.
* tests: test for list of Obs to sql added.
* feat: auto_gamma functionality added for deserialization of lists of
Obs.
