Energyflow

- Reintroduced EFMs, with full documentation, testing, and integration with the core EFP code.
- Fixed bug in qg_nsubs where `cache_dir` was set to `None` which caused an error. Thanks to Serhii Kryhin for catching this!
- Fixed bug where `emd` module could modify the inputs in place.
- Changed the `emds` function to use global arrays in order to consume less memory when using multiple jobs.
- Updated the `eval_filters` method of the `EFN` class to adjust for new Keras behavior.
- Implemented the `D2`, `C2`, and `C3` observables using EFPs.
- Two new demos, [EFM Demo](/demos/efm-demo) and [Counting Leafless Multigaphs with Nauty](/demos/counting-leafless-multigaphs-with-nauty).


0.13.x

- Keras 2.2.5 fixes a bug in their `batch_dot` function that is used by their `Dot` layer which is used by the `EFN` and `PFN` classes. This necessitates adjusting our code to account for the new behavior.

- When loading MOD HDF5 files, jets are now made from copies of the particle arrays rather than from views,
enabling the large arrays to be freed and only the selected jets to remain in memory (which can have substantial memory savings).

- Added support for downloading and reading MOD datasets containing CMS Open Data and Simulation from Zenodo.
- EMD module now has support for spherical measure.
- Added particle utility functions to map PDG IDs to electric charges.
- Added `sum_ptyphims` and `sum_ptyphipids` functions to sum four-vectors given in hadronic coordinates.
- Added scheme choices for summing four-vectors of particles.
- Added preprocessing functions to particle utilities, including `center_ptyphims`,
`rotate_ptyphims` and `reflect_ptyphims`.
- A `~` is now expanded to the user's home directory properly in the `filepath` option to architectures.
- Added `h5py` install dependency for MOD Datasets.
- Improved binder environment with fastjet, latex, and default matplotlib settings.
- Added observables submodule which currently includes image_activity and zg.
- EMD module now imported when importing toplevel energyflow.


0.12.x

- Set allow_pickle to True explicitly in Generator (recently changed default in NumPy).
- Added Herwig7.1 dataset to `qg_jets`. A big thanks to Aditya Pathak for generating these Herwig samples!
- Quark and gluon dataset files can now be obtained from Zenodo in addition to Dropbox.
- Changed internals of EFN to use standalone functions for easier use of subnetwork components.
- Added some particle utility functions to deal with PDG IDs.
- Added particle utilities to deal with pseudorapidities.
- Changed `gen_random_events_mcom` to have positive energies (momenta still sum to zero).
- Added l2 regularization to layers in EFN and PFN architectures. Thanks to Anders Andreassen for submiting this pull request!
- Added tests for particle utils.
- Particle utilities now accept arrays of events.

- Added another periodic phi test for event EMD.
- Changed gdim default to None (to reduce potentially unexpected behavior).
- Increased numerical stability of EMD computation by including an internal change of units.
- Added verbosity functionality to EFP Generator.