Refactor out `_tofile`/`_fromfile` from `DirectoryStore`#503

Merged

jrbourbeau merged 7 commits intozarr-developers:masterfrom

jakirkham:ref_tofile_fromfile

Nov 12, 2019

Commits on Nov 8, 2019

Commits on Nov 11, 2019

Commits on Nov 12, 2019

Adds release notes entry
jrbourbeau
committed