Hfexcel

Change Log:
- Enable `schema` parameter for `HFExcelWorkbookFilter` to pass custom schema into `jsonschema.validation`.

Change Log:
- Add jsonschema validation https://github.com/Julian/jsonschema

Change Log:
- Add `width` parameter to `HFExcelRow` class. If 0 or None, it will be set to 1. If greater than its column's width, columns width will be set.
- Update `HFWorkbookFilter` regarding parameter change.

Change Log:
- Rename`utils.py` to `models.py`
- Rename `HFExcelWorkbook().helper` to `HFExcelWorkbook().filter()` and make it chainable (e.g: `HFExcelWorkbook().filter().populate_xxx_json().populate_xxx_json()`
- Make `HFExcelStyle` helper methods chainable (e.g: `add`, set_defaults`)
- Fix bug where Column parameter was missing

Styling fix

0.0.5-latest
Change Log:
- Add `hide_header` parameter to HFExcelColumn. `True` collapses the header, `False` displays the header. Default: `False`