Pzflow

Release of PZFlow 3.0.0 (the 0.0.1 was just to fix the README on PyPI and doesn't reflect any changes to the code)

Changes
- Made Uniform the default distribution
- Made all distributions symmetric about zero
- Moved to Optax for optimization
- Added default bijectors to `Flow` and `FlowEnsemble`.

Features
- Added early stopping to train methods
- Added progress bar to train methods
- Added `CentBeta13` distribution, which looks like a Guassian with hard cutoffs.

Bugs
- Fixed bug where `FlowEnsemble` metadata was not available from the ensemble itself, only from the individual flows in the esemble

- Made some fixes so that pzflow works with the latest version of jax
- I had to change the Uniform Dequantizer so that you always have to specify which columns to dequantize

Fixed error where marginalization yields NaNs when combined with error convolution.

Fixed error where example files weren't included in release v2.0.1