Added
- Added `rit` (render if true) to `var` template tag.
- Added `rif` (render if false) to `var` template tag.
- Added `rin` (render if none) to `var` template tag.
Changed
- `get_var` tag has changed its name to `var`.
- Now `update` method of `Variable`'s `QuerySet` supports `value` kwarg.
- `Variable` now has a default primary key implementation.