* jug shell: Add `get_filtered_tasks()`
* jug: Fix `jug --version` (which had been broken in the refactoring to
use subcommands)
* jug shell: Fix message in jug shell when there are no dependencies (it
would repeatedly print the message stating "this will only be run once")
* jug pack: Make it much faster to invalidate elements
* file_store: ensure that the temporary directory exists
* jug: Drops support for Python 3.4