Django-tables2

- Return `None` from `Table.as_values()` for missing values. [419](https://github.com/bradleyayers/django-tables2/pull/419)
- Fix ordering by custom fields, and refactor `TableData` [424](https://github.com/bradleyayers/django-tables2/pull/424), fixes [#413](https://github.com/bradleyayers/django-tables2/issues/413)
- Revert removing `TableData.__iter__()` (removed in [this commit](https://github.com/bradleyayers/django-tables2/commit/8fe9826429e6945a9258bc181fcbd711b282dba9)), fixes [#427](https://github.com/bradleyayers/django-tables2/issues/427), [#361](https://github.com/bradleyayers/django-tables2/issues/361) and [#421](https://github.com/bradleyayers/django-tables2/issues/421).

- Implement method `Table.as_values()` to get it's raw values. [394](https://github.com/bradleyayers/django-tables2/pull/394) by [intiocean](https://github.com/intiocean)
- Fix some compatibility issues with django 2.0 [408](https://github.com/bradleyayers/django-tables2/pull/409) by [djk2](https://github.com/djk2)

- Documentation for `None`-column attributes [401](https://github.com/bradleyayers/django-tables2/pull/401) by [dyve](https://github.com/dyve)

- `None`-column attributes on child class overwrite column attributes of parent class [400](https://github.com/bradleyayers/django-tables2/pull/400) by [dyve](https://github.com/dyve)

- Apply `title` to a column's `verbose_name` when it is derived from a model, fixes [249](https://github.com/bradleyayers/django-tables2/issues/249). ([#382](https://github.com/bradleyayers/django-tables2/pull/382) by [shawnnapora](https://github.com/shawnnapora))
- Update documentation after deprecation of `STATIC_URL` in django ([384](https://github.com/bradleyayers/django-tables2/pull/384), by [velaia](https://github.com/velaia))
- Cleanup of the templates, making the output more equal ([381](https://github.com/bradleyayers/django-tables2/pull/381) by [ralgozino](https://github.com/ralgozino))
- Use new location for `urlresolvers` in Django and add backwards compatible import ([388](https://github.com/bradleyayers/django-tables2/pull/388) by [felixxm](https://github.com/felixxm))
- Fix a bug where using `sequence` and then `exclude` in a child table would result in a `KeyError`
- Some documentation fixes and cleanups.

- Added `get_table_kwargs()` method to `SingleTableMixin` to allow passing custom keyword arguments to the `Table` constructor. ([366](https://github.com/bradleyayers/django-tables2/pull/366) by [fritz-k](https://github.com/fritz-k))
- Allow the children of `TableBase` render in the `{% render_table %}` template tag. ([377](https://github.com/bradleyayers/django-tables2/pull/377) by [shawnnapora](https://github.com/shawnnapora))
- Refactor `BoundColumn` attributes to allow override of CSS class names, fixes [349](https://github.com/bradleyayers/django-tables2/issues/349) ([#370](https://github.com/bradleyayers/django-tables2/pull/370) by [graup](https://github.com/graup)). Current behavior should be intact, we will change the default in the future so it will **not** add the column name to the list of CSS classes.