General refactor of codebase with removal of Python 2 support. This will allow yahoo-historical to adopt more modern features such as f-strings and type hints.
This update also creates a new `as_dataframe` field, allowing developers to opt out of the Pandas DataFrame response.
0.4.1
0.4.0
0.3.2
0.3.1
0.3.0
Fixes bug with conda environment and added requirements.txt