Uproot

Fixes 294 with 295: `uproot.pandas.iterate` assumes Python 3's absolute imports, so for Python 2 to work, we need

python
from __future__ import absolute_import


at the top of every file in uproot. (Thanks, chrisburr!)

PR 293 (on master, not back-propagated).

Full release with lazy profiles ([see pre-release announcement](https://github.com/scikit-hep/uproot/releases/tag/3.7.0rc1)).

First version with lazy profiles:

python
a = uproot.lazyarrays("nanoaod*.root", "Events", profile="cms.nanoaod")
a.electrons jagged array of electron objects
a.electrons.pt jagged array of electron pT
a.electrons.photon jagged, masked array of the photons linked to each electron (if any)
a.electrons.photon.pt their pT
a.photons.pt this is different


The profile restructures the lazy array so that—without triggering any reads—it has a physics-friendly nested structure.

Can now write LZ4-compressed data (PR 288).

Updated front-page documentation. New version to copy it to PyPI.