version bump 0.15.6: niggles from 2012

- CFB prevent infinite loop (h/t @rossj)
- pass updated eslint checks (fixes #1726 h/t @BjoernRave)
- defined name proper encoding (fixes #1785 h/t @laohe98)
- correct theme color order (fixes #389 h/t @foreverpw)
- ODS / XLML more aggressive flagging of stub cells
- cellStyles implies sheetStubs
- updated SSF to 0.10.3