Merge pull request #304 from LeszekSwirski/dist-test-win

Make skulpt dist/test work on Windows
Add yield suspensions (soft timeout)
Correct codegen with dumpJS on
Add default handler for Sk.yield
Fix setTimeout exists check in time
Return null/false from suspension handler to perform default action.
Add option for handling any suspension to asyncToPromise

Allows the user to perform an action on any suspension, useful e.g. for threading.
Merge branch 'yield-suspension'