- Remove `from_xls` and `from_xlsx`.
- Add `headers` support to `File_Format.Excel`.
- Altered default read for Excel to be the first sheet.
- Altered behavior so that single cells grow down and right when reading sheet.
- Altered `Excel_Range` so knows if single cell or 1x1 range address.
# Important Notes
- Renamed `Range` to `Cell_Range` to avoid name clash.
