Version 7.7.0

Bug fixes

Take the sum instead of the max in dir_size(). Incurs rehashing for some workflows, but should not invalidate any targets.

Add a new which_clean() function to preview which targets will be invalidated by clean() (#1014, @pat-s).
Add serious import and export methods for the decorated storr (#1015, @billdenney, @noamross).
Add a new "diskframe" format for larger-than-memory data (#1004, @xiaodaigh).
Add a new drake_tempfile() function to help with "diskframe" format. It makes sure we are not copying large datasets across different physical storage media (#1004, @xiaodaigh).
Add new function code_to_function() to allow for parsing script based workflows into functions so drake_plan() can begin to manage the workflow and track dependencies. (#994, @thebioengineer)