Support explicit passing of data between tasks

[sportsracer]

Have a look at the GitHub stats download example ... It needs to store data in a temp file to pass it between tasks.

Support explicit in-memory passing of data between dependencies and tasks. This will need modifications to the Task interface!

[scoder]

The example link in the ticket description gives a 404. I guess it should be "https://github.com/trustyou/dagger/blob/master/examples/github_stats.py".