Awkward

As discussed in 350, Awkward arrays can no longer be used as Pandas columns. Also part of this API change (464),

* `array.tojson` has been removed: use `ak.to_json(array)`.
* `array.columns` has been renamed: use `array.fields`.
* `ak.keys(array)` has been renamed: use `ak.fields(array)`. (`ak.keys` still exists with a "deprecated until 0.4.0" message)
* `array.ndim` (property) is now the dimension of the array, rather than `1` (a Pandas requirement)
* `array.type` has been added; it is equivalent to `ak.type(array)`. If you had fields named `"type"`, they will now have to be accessed as `array["type"]`, rather than `array.type`.

Thanks to reikdas, this is the first release with a [formal specification](https://github.com/scikit-hep/awkward-1.0/blob/master/kernel-specification.yml) for the cpu-kernels/cuda-kernels library! (The bottom layer of the 3-layer architecture, [documented here](https://awkward-array.readthedocs.io/en/latest/_auto/kernels.html).)

Furthermore, ufunc behavioral matching has been generalized (463) to allow:


ak.behavior[np.multiply, numbers.Number, "Vector"] = scalar_multiply
ak.behavior[np.multiply, "Vector", numbers.Number] = scalar_multiply


Two mistakes were fixed in the Windows builds (465 by chrisburr and 467), allowing them to be used without debug-version system libraries (430). The first of these enabled lgray to [deploy it on conda-forge](https://anaconda.org/conda-forge/awkward1)!

Still built on pybind 2.4.3, though we might want to update that, especially if pybind supports the NumPy datetime dtypes.

Getting closer to finalizing reikdas and trickarcher's work this summer, and nsmith- fixed a missing case in `ak.type` (booleans!).

Also, the Windows build procedure was generalized to allow awkward1 to become a package on conda-forge.

ianna fixed the intermittent MacOS error (issue 320)! Although this bug only manifested itself on MacOS in our tests, due to the capriciousness of memory overwriting/reading, it was really a bug on all platforms.

reikdas auto-generated more CUDA kernels and will now be turning to consolidating what we have (i.e. cleanup). 59 of the 77 embarrassingly parallel kernels can be converted without manual intervention.

jpivarski fixed a bug in ak.flatten and ensured that variable dimensions remain variable and regular dimension remain regular in reducers, unless there are missing values involved. I also added two performance improvements: broadcasting only compacts lists if they have to, resulting in a 40× speedup in the limit of large arrays (PR 444) and when Uproot has types that would be slow to deserialize from ROOT, it can now offload the processing to a C++ loop in Awkward, resulting in an 80× speedup in the targeted case (PR 448). This required ak.concatenate to merge in batches, rather than two at a time (TBaskets in a ROOT file present hundreds of arrays to concatenate; an _O(n²)_ algorithm is bad), which is PR 449 (merged into PR 448 before the latter was squash-and-merged).

reikdas has added a second batch of CUDA translations.

<img src="https://user-images.githubusercontent.com/1852447/92425142-f7c5d480-f14b-11ea-8268-87672d6b824b.png" width="600">

nsmith- fixed reference-cycle issues in VirtualArrays by making ArrayCache keep only a weak reference to the cache (that it might be included in).

jpivarski fixed some odds and ends and also revamped the deployment procedure so that `pip install awkward1` doesn't install anything outside of its Python directory. (Homebrew complains about that on MacOS.) There is now a `python -m awkward1.config --cflags --libs` command to get a path to the installed header files and libraries, and `dependent-project` is now being tested regularly on Linux and MacOS.

Quick fix for inability to print out partitioned arrays.

trickarcher added conversions to and from CuPy arrays, enabling all of CuPy's ufuncs for non-structure-changing math (i.e. formulas). (372)

reikdas improved the kernel testing (412, 413, 414).

jpivarski fixed references to `np.object` (where `np` is `NumpyMetadata`, not `numpy`), which was breaking Uproot4 tests and motivated this new release.

jpivarski also fixed 415, issues with `ArrayBuilder.append` and union types.