record-replay, pre-post test files

Record-Replay:

Fixed some instrumentation issues that prevented tracing of function calls
Added multi-file tracing, so replays correctly traverse through user workspace files
Cleared up some potential issues like lambdas, comprehension variables, etc

Pre and Post test files

Authors can add __pre.py and __post.py files to test cases
These files are run with individual tests and share state with main.py either before or after
When in author mode, running tests will surface better errors from tests with pre and post files to help with debugging