Awkward

Minor changes, but one is a feature, not a bug-fix, so it needs to be pre-released before 1.1.0. I need to get 1.1.0 out soon, but I want the Parquet stuff to be in it.

Can now read and write Parquet datasets (conventions for sets of multiple files): PR 706, fixes 368 (old!).

Also, Python 2 can use ellipsis because we have pybind11 2.6 now: PR 707, fixes 705.

More minor bug fixes, mostly related to partitioned arrays and Parquet files: PRs 703 and 699.

Actually remove the features that have been deprecated, [scheduled to be removed in 1.1.0](https://github.com/scikit-hep/awkward-1.0#roadmap): PR 698.

Fixed 689, the dimension of arrays returned by empty slices: PR 691.

ianna fixed tuple-building in ArrayBuilder to guard against specifying a nonexistent slot and segfaulting: 697.

Various fixes in preparation for a SciPy 2021 tutorial:

* Added [ak.materialized](https://awkward-array.readthedocs.io/en/latest/_auto/ak.materialized.html) to force-materialize arrays (opposite of [ak.virtual](https://awkward-array.readthedocs.io/en/latest/_auto/ak.virtual.html)) because debugging very lazy deferments is hard.
* Can now use `np.newaxis` to give one array the same number of dimensions as another for slicing (which closes 492).
* Fixed `ak.min`/`ak.max` with `axis != None` for partitioned data.
* Fixed a bug that affected boolean-masking of partitioned data.

Reducing over-materialization of virtual arrays: PRs 643, 644, 657, added Form-aware lazy Parquet: 688

Fixed `ak.from_buffers` to allow unreachable elements: PR 673

Developed the AwkwardForth VM: PRs 683, 648, 653, 661, 664, 672

Removed right-broadcasting from all operations except those that require it for NumPy compliance: 656, 680

ianna improved sorting: PRs 639, 687, added complex numbers support: PRs 652

trickarcher generalized CuPy interop to JAX: PRs 645, 662

reikdas cleaned up developer scripts: PRs 665, 666, 667

henryiii added more code quality tests: PRs 675, 681, 682, 677, 676, 685, 683

Cleaned up documentation: PRs 647, 650, 684

nsmith- fixed virtual arrays in `ak.to_arrow` (PR 642).

Otherwise, this is identical to 1.0.2rc5.

Fixed 628, allowing `np.int64(N)` to be used in a slice like integer `N` (PR 636).

The intent is for this to be the last prerelease before 1.0.2. Test it!