This commit contains the following:
* New data types to support full tracebacks
* New traceback data type used across stl and ast
* Updates to tests
* fixes for error messaging in sym and some stl functions
* env prints variables and functions in seperate columns
* run/stl seperation of concerns significantly better
* def doesnt store lists or lambdas in the environment
* Background task implementation
* Foreground an existing task implementation
* Documentation for both
* Refactors to signal handling, process pre-exec
