Uproot

douglasdavis fixed a bug in which TArrayDs were assumed to be NumPy arrays (with a `reshape` method).

nsmith- ported the Uproot 3 "clusters" function, now named `common_entry_offsets`. He also prompted me to fix my use of units: MB vs MiB.

I revamped the physical layer to match the way it's actually used in the higher-level code. It's about half as many lines as before. (No longer duplicating thread-handling in vector-read and multipart classes; it's all handled by executors now.)

Fixed an HTTP-freeze issue (fallback method wasn't informed that it needs to notify when done) discovered when writing Awkward tutorials.

Fixed scikit-hep/uproot513.

Histogram conversion methods are now `to_numpy()`, `to_boost()`, and `to_hist()` (with parentheses). Also fixed 47.

Histograms have conversion properties to NumPy and boost-histogram.

Fixes 42.