fill the colon-style text inside css replacements.
this allows copy & paste to get back the colon version so you can then paste and get back what you copied if you're following the suggested flow
when replacing with native codepoints, check it's one that's defined, else drop through to css/img/text.
not every emoji is supported by every encoding.
detect self.supports_css so that if we drop past a native replacement (because a codepoint is not supported) we can fallback to css instead of images
rebuilt js file