Pachyderm

Added

- `recursive_getitem` to retrieve an item from a recursive dict. In principle, this should also work for other
objects which implement `__get_item__(...)`, but it is not tested for those other objects. See:
`5982c6bfd5a13a4b8f09464ca27ac24ba8477f6f` and `a3653859c94bc892082842ecc7997e4facda1e60`.

Changed

- Relaxed some `Dict` -> `Mapping` typing information where possible for greater compatibility with inputs.
See: `53ae9f762f344978161ff662226f7fa9202c8b84`.

Fixed

- Don't modify the passed analysis iterables when iterating with
`iterate_with_selected_objects_in_order(...)`. See: `7daf01ea590e9ccbdc6511d6a5379757409537fa`.
- Indicate that the package is typed (it already was, but the typing wasn't being checked in downstream
packages). See: `409922e80541155d414c2c101eb913b4ab9fd9ac`.
- Improved typing information in the `histogram` module. See: `dded82643a8c7c7acc684d64c958eed63c84b3e6`.
- Improved typing information in the `generic_config` module. See: `c9a8f57fea5f72e62841f264d768e785cd6da3c5`,
and `03ad1faf0cb295c7387badd1e59082c5740fbdfb`.

Added

- `Histogram1D` operators (add, subtract, multiply, divide) with other hists, including error propagation. These
operations were confirmed by comparing against the same operations in ROOT histograms (it turns out that the
error propagation is exactly as expected, but the ROOT code was sometimes difficult to interpret). See:
`052ea365e4e6a8a4d6bce38779ed9fe2edcfc089` and `7df8ceaa445d5c7aea4c62f6b32bc198eb59ccc3`.

Changed

- Refactor `KeyIndex` creation into a separate function so it can be accessed by other packages. In
particular, this allows for their creation (with the iterable field access, etc) from analysis packages.
See: `d821908c80e5e81df43986cb0831f112b706b91b`.

Added

- Added iterator (`__iter__`) over names and values to the `KeyIndex` object. See:
`a7dfa745aefbc381a245017dbde722f368ad39de`.

Fixed

- Added `__init__.py` to the `tests` directory. Otherwise, test fixture discovery sometimes fails. See:
`c1a1f059e2c921f5e1afb3dfc9dc5624a2754596`.