Re-enable doctests

[cclauss]

Add scripts/run_doctests.sh to run Python doctests on both Python 2 and 3.

Fixes #3586, #3659, #3673 which got into bad git states because of `vendors/infogami".

Output:

495 passed, 25 skipped, 10 xfailed, 35 warnings in 87.36s (0:01:27)

Technical

Passing these tests required several absolute import changes, etc.

Testing

Yes! 495 of them.

Screenshot

Stakeholders

[cclauss]

Which files would it make sense to remove from this PR to make it easier to review and merge?

Please check the files that you want me to remove...

• openlibrary/api.py
• openlibrary/catalog/amazon/parse.py
• openlibrary/catalog/marc/build_record.py
• openlibrary/catalog/marc/read_toc.py
• openlibrary/catalog/merge/build_db.py
• openlibrary/catalog/merge/load_from_json.py
• openlibrary/catalog/merge/merge_bot/bot.py
• openlibrary/catalog/merge/merge_bot/merge.py
• openlibrary/catalog/merge/merge_index.py
• openlibrary/core/helpers.py
• openlibrary/core/seq.py
• openlibrary/data/__init__.py
• openlibrary/data/dump.py
• openlibrary/data/solr.py
• openlibrary/olbase/events.py
• openlibrary/plugins/akismet/code.py
• openlibrary/plugins/importapi/metaxml_to_json.py
• openlibrary/plugins/openlibrary/support.py
• openlibrary/plugins/upstream/account.py
• openlibrary/plugins/upstream/code.py
• openlibrary/plugins/upstream/tests/test_utils.py
• openlibrary/plugins/upstream/utils.py
• openlibrary/solr/solrdump.py
• openlibrary/solr/update_work.py
• openlibrary/templates/type/edition/view.html
• openlibrary/utils/__init__.py
• openlibrary/utils/dateutil.py
• openlibrary/utils/form.py
• openlibrary/utils/httpserver.py
• openlibrary/utils/schema.py
• scripts/solr_builder/solr_builder/solr_builder.py
• scripts/solr_builder/solr_builder/solr_builder_main.py

[mekarpeles]

These changes look okay to me.