Pretty Tracebacks and Concurrency

This release adds the following features:

• util.highlight_current_function: Called from within a bound MetaFunction, returns a string identifying where in the function pipeline the function is.
• Pretty tracebacks: By default, function location is appended to exceptions in child functions, using the above method
• util.concurrent and the concurrent module: Add a subclass of FunctionMerge that executes each of its functions in parallel.