Django-bootstrap5

- Switch to a [CalVer](https://calver.org) YY.MINOR versioning scheme. MINOR is the number of the release in the given year. This is the first release in 2021 using this scheme, so its version is 21.1. The next version this year will be 21.2. The first version in 2022 will be 22.1.
- Update Bootstrap to 5.1.3 (167, 194).
- Add support for Django 4 and Python 3.10 (193).

- Fix disabled parameter for RadioSelect and CheckboxSelectMultiple (163).

- Respect safe strings in bootstrap_messages (145).

- Bump Bootstrap from 5.0.1 to 5.0.2 (138).

- Fix bug in exclude handling (124).

- Use `wrapper_class` and `inline_wrapper_class` for spacing (113).
- Document known issue with `RadioSelectButtonGroup` (114).
- Bump Bootstrap from 5.0.0 to 5.0.1 (110).
- Fix validation HTML for checkbox and radio select (92).
- Ignore placeholders in attributes in render_tag (103).
- Update default Bootstrap to 5.0.0 (97).
- Fix issue where error messages were not displayed for input groups.
- Introduce `server_side_validation` setting for controlling Bootstrap 5 server-side validation classes (90).
- Use `success_css_class` instead of `bound_css_class`.
- Use standard Exception classes (83).
- Support `extra_classes` in `render_alert` (81).
- Do not apply `mark_safe` to content for `bootstrap_button`.
- Add keyword arguments to `bootstrap_button` tag (79).
- Add size parameter to example forms (77).