Intermittent Transaction Bug Fix

Fixes an error caused by a redundant transaction operation that was reported to fail intermittently in a multithreaded use case. Thanks @Krisscut for reporting the issue and testing the fix.

#8

The release also migrates the build to GitHub Actions, reports test coverage to Code Climate, and increases the test coverage.

Thread Safety

Restore the original locking block, setup thread-safe defaults for sqlite, and add unit tests for threaded use.

Sliding Log and Persistence

Change the rate limiting strategy from fixed windows to a sliding log. Back the log with sqlite and allow it to be persisted to disk easily.