* Perserve flags in EntityRuler
The EntityRuler (explosion/spaCy#3526) does not preserve
overwrite flags (or `ent_id_sep`) when serialized. This
commit adds support for serialization/deserialization preserving
overwrite and ent_id_sep flags.
* add signed contributor agreement
* flake8 cleanup
mostly blank line issues.
* mark test from the issue as needing a model
The test from the issue needs some language model for serialization
but the test wasn't originally marked correctly.
* remove unneeded model loading
The model didn't need to be loaded, and I replaced it with
a change that doesn't require it (using existings fixtures)
* change tempdir handling to be compatible with python 2.7
* Adds code to handle item saved before this change.
This code chanes how the save files are handled and how the bytes
are stored as well. This code adds check to dispatch correctly
if it encounters bytes or files saved in the old format (and tests
for those cases).
* use util function for tempdir management
Updated after PR comments: this code now uses the make_tempdir function from util
instead of doing it by hand.
