Crispy-forms-gds

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* Added hints to checkboxes and radios.
* Added contents summary to Accordion component sections.
* Added the fields and templates needed for the Date input component.
* Added template tags for back links, start buttons and breadcrumbs.
* Added a production-ready base template that can be used in sites.
* Added a Choice class to make setting hints and dividers on checkboxes and radio buttons cleaner and easier.
* Merged the templatetags so all you have to do is {% load crispy_forms_gds %}.
* Changed Table component to support a caption and CSS styling.
* Deleted the hints attribute on Field.checkboxes() and Field.radios()

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- Added all the form-level components from the Design System. The only one missing is Date input.

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- Added all the project files needed to generate the package documentation.
- Added all the project files needed to release the package to PyPI.
- Added a set of core templates for rendering forms.
- Added layout object for rendering submit buttons.
- Added tests for verifying text inputs are rendered correctly.
- Added Django site for showing how the forms are used.