Moved the check for empty step name to take place at step generation instead of example table value substitution
Allow emtpy doc string and data table entries from outlines

After token replacement for instantiated scenarios from scenario
outlines, the doc string and data table entries are allowed to be
emtpy. The step itself on the other hand, must be non-empty.
Merge branch 'LeonPoon:blank-table-cell-after-substitution'
Merge #709 and #713. Update History.md