#22 Enhancement: Emoji reader

A lot of flavors support syntax like `:smile:` to insert an emoji. Concerns/challenges: * Emoji characters are a fast moving target. Could make maintaining difficult. * How are combining forms (e.g. skin tone) handled in flavors that support this? * Support for custom emoji names and images * Optional large forms when used alone or on a line alone * Would strongly suggest a mechanism for autocompletion, or at least hooks for someone else to implement and be able to query the lookup table * Need to support synonyms. E.g. `:detective:` and `:spy:` both pulling up 🕵️. One name should be the canonical one.