Provide Twig functions and tokens, remove dependency on Date Augmenter API

Problem/motivation

The Calendar Link module → provides Twig functions instead of directly modifying the output of date fields as part of the rendering process. This module could (potentially) offer the same capability (in addition to the Date Augmenter implementation), at which point it wouldn't be necessary for a site to use the Date Augmenter API to use this module.

This module could similarly provide tokens to allow generating the markup in other places. It might need a wider set of tokens to provide the same range of output options.

Proposed resolution

Investigate if the same results could be achieved using one or more Twig functions. If so and the effort is not excessive, provide this capability.