Django-tables2

- Added `as=varname` keyword argument to the `{% querystring %}` template tag,
fixes [481](https://github.com/jieter/django-tables2/issues/481)
- Updated the tutorial to reflect current state of Django a bit better.
- Used `OrderedDict` rather than `dict` as the parent for `utils.AttributeDict` to make the rendered html more consistent across python versions.
- Allow reading column `attrs` from a column's attribute, allowing easier reuse of custom column attributes (fixes [241](https://github.com/jieter/django-tables2/issues/241))
- `value` and `record` are optionally passed to the column attrs callables for data rows. [503](https://github.com/jieter/django-tables2/pull/503), fixes [#500](https://github.com/jieter/django-tables2/issues/500)

- Added a `row_counter` variable to the template context in `TemplateColumn` (fixes [448](https://github.com/jieter/django-tables2/issues/488))

- Do not fail if `orderable=False` is passed to `ManyToManyColumn()`

- Added `separator` argument to `ManyToManyColumn`.
- Allow `mark_safe()`'d strings from `ManyToManyColumn.tranform()`
- Disabled ordering on `ManyToManyColumns` by default.

- Made positional `data` argument to the table `__init__()` a keyword argument to make inheritance easier. Will raise a `TypeError` if omitted.

- Allow export file name customization [484](https://github.com/bradleyayers/django-tables2/pull/484) by [federicobond](https://github.com/federicobond)
- Fixed a bug where template columns were not rendered for pinned rows ([483](https://github.com/bradleyayers/django-tables2/pull/483) by [khirstinova](https://github.com/khirstinova), fixes [#482](https://github.com/bradleyayers/django-tables2/issues/482))