Careless

The previous version of `careless` would pull the latest release of TensorFlow which was often a release candidate. This sometimes breaks compatibility with CUDA on making it impossible to train on GPU. This release restricts TF to major versions which are more stable.

This release reverts an earlier change which made the slower eager execution the default during training and inadvertently flipped the semantics of the `--run-eagerly` flag. There are no new features or CLI changes to note. Users will notice much faster training however.

This version fixes the numerical instability issue introduced in v0.2.1 (61). This version adds a new command line parameter `--epsilon` which controls the minimum width of variational distributions. The default value of `1e-7` should be fine for most any data.

New Feature: Saving and loading weights in v0.2.1
- Output neural network weights to {output_prefix}_scale
- Output structure factor distribution weights {output_prefix}_structure_factor
- Load previous structure factors with `--structure-factor-file=`
- Load previous neural network weights with `--scale-file=`
- Freeze structure factors with `--freeze-structure-factors`
- Freeze neural network scales with `--freeze-scales`

Minor changes
- Switch all bijectors to `Exp` rather than `Softplus`
- Print a version number at run time
- Report the log likelihood of test sets
- Initialize the variational distribution to match the width of the prior
- Add CLI flag to control this initial width
- Add a tensorflow implementation of the fourth moment of truncated normals

Bug fixes
- Fixed a bug in metric reporting which lead to incorrect KL Divergences in the history
- Fix a bug whereby the second moment of the predicted intensities was inaccurate

This version is a complete rewrite relative to the previous release. There is very little that this release doesn't touch. It is not safe to assume the CLI arguments are the same. Many features from the previous version (like reference priors) have been removed. If you rely on these for your work, please
- continue to use the previous version
- file an issue

I will make every effort to reintroduce the feature.

This is the latest version of the original `careless` implementation. This release is being made for debugging purposes.