Fix/discrete log async

[danwallach]

Issue

Fixes #130

Description

I'm working on getting EG to work with ray.io, a cluster computing framework. I ran into one issue with async code in dlog.py. The gist of it is that the call to initialize __dlog_lock was failing, and I was getting an error about a missing "event loop". Turns out, the way Ray was running the code was tickling this issue.

The solution is really straightforward: delay initialization of the lock variable until you're inside __discrete_log_internal.

Testing

The existing test suite still works fine.

Checklist

🚨Please review the guidelines for contributing to this repository.

• 🤔 CONSIDER adding a unit test if your PR resolves an issue.
• ✅ DO check open PR's to avoid duplicates.
• ✅ DO keep pull requests small so they can be easily reviewed.
• ✅ DO build locally before pushing.
• ✅ DO make sure tests pass.
• ✅ DO make sure any new changes are documented.
• ✅ DO make sure not to introduce any compiler warnings.
• ❌AVOID breaking the continuous integration build.
• ❌AVOID making significant changes to the overall architecture.

💚Thank you!

[danwallach]

Need to rebase this before merge. The change here is way too big.

[danwallach]

Okay, rebase successful. The PR now only touches dlog.py.

[keithrfung]

Changed this to ready for review and left comments since this seemed as if the changes were already implemented.

[AddressXception]

modified the comment lines to be more concise in code, and moved the description into the PR. Everything is ready to go