Uproot

Fixes 64: `TDirectoryFile` should be treated the same way as `TDirectory`. Files made with `TDirectoryFile` now work.

Fixed a small but crucial bug in calculation of TLorentzVector mass.

Fixes 63 by adding another way to recognize `std::string` branches.

This release was created merely to test PyPI deployment; I need to verify that my keys are still okay.

Now uproot is supported on PyPy v5.9 and up because this version of PyPy has a working Numpy implementation.

The only missing piece was `sys.getsizeof`, which `MemoryCache` uses to determine when to evict old entries from the cache, but PyPy refuses to implement because it's not well defined. (It's admittedly heuristic for `MemoryCache`, but errs on the side of being conservative.) I added a work-around `sys.getsizeof` for PyPy so that `MemoryCache` behaves the same way as it does in CPython, even if the actual memory use before evicting is only approximate.

Make JaggedArrays pickleable, in response to closed PR 62.