Feature Request: Include Date Formatting in Template Engine

[MizterB]

Per discussion here:

https://community.home-assistant.io/t/custom-secondary-info-for-entities-card/82551/40

parseTemplate() provides flexibility in exposing last_changed, last_updated, and any timestamps that may exist in an entity's attributes. However, timestamps are displayed in ISO18061 format, which is not terribly front-end friendly.

Would it be possible to extend the template parsing engine to allow for custom date formats? Both absolute and relative times would be ideal, possibly following (or using) the examples in Moment.js?