Ctgan

In this release we introduce several minor improvements to make CTGAN more versatile and
propertly support new types of data, such as categorical NaN values, as well as conditional
sampling and features to save and load models.

Additionally, the dependency ranges and python versions have been updated to support up
to date runtimes.

Many thanks fealho leix28 csala oregonpillow and lurosenb for working on making this release possible!

Improvements

* Drop Python 3.5 support - [Issue 79](https://github.com/sdv-dev/CTGAN/issues/79) by fealho
* Support NaN values in categorical variables - [Issue 78](https://github.com/sdv-dev/CTGAN/issues/78) by fealho
* Sample synthetic data conditioning on a discrete column - [Issue 69](https://github.com/sdv-dev/CTGAN/issues/69) by leix28
* Support recent versions of pandas - [Issue 57](https://github.com/sdv-dev/CTGAN/issues/57) by csala
* Easy solution for restoring original dtypes - [Issue 26](https://github.com/sdv-dev/CTGAN/issues/26) by oregonpillow

Bugs fixed

* Loss to nan - [Issue 73](https://github.com/sdv-dev/CTGAN/issues/73) by fealho
* Swapped the sklearn utils testing import statement - [Issue 53](https://github.com/sdv-dev/CTGAN/issues/53) by lurosenb

Minor version including changes to ensure the logs are properly printed and
the option to disable the log transformation to the discrete column frequencies.

Special thanks to kevinykuo for the contributions!

Issues Resolved:

* Option to sample from true data frequency instead of logged frequency - [Issue 16](https://github.com/sdv-dev/CTGAN/issues/16) by kevinykuo
* Flush stdout buffer for epoch updates - [Issue 14](https://github.com/sdv-dev/CTGAN/issues/14) by kevinykuo

Reorganization of the project structure with a new Python API, new Command Line Interface
and increased data format support.

Issues Resolved:

* Reorganize the project structure - [Issue 10](https://github.com/sdv-dev/CTGAN/issues/10) by csala
* Move epochs to the fit method - [Issue 5](https://github.com/sdv-dev/CTGAN/issues/5) by csala

First Release - NeurIPS 2019 Version.