Feature release

Features

• Add type hints for run_sync (#322)
• Use tblib to enable pickling of tracebacks between processes. Mainly, this preserves context of exceptions including chained exceptions. (#323)

Bugfixes

• Prevent Ctrl+C from inducing various leaks and inconsistent states. (#239)
• Cleaned up names/qualnames of objects in the trio_parallel namespace. (#291)

Deprecations and Removals

• Removed python 3.6 support (#236)