Fixes #91... I think? Well anyway, it fulfils my use case, maybe @killroy42 can feedback as to whether it fulfils theirs. Notably, it always maps the matched emoji to the relevant icon file name, such that e.g. if "ABC" is matched as an emoji, it always becomes 41-42-43.png or 41-42-43.svg. Supplying custom mappings is not supported, but a future PR could build on this one to enable that if it's desirable.

Perf should remain near-identical for cases where the default regex is used, with a small performance hit in cases where a customized regex is supplied. This is due to the XSS-prevention logic, which is assumed unnecessary with the default regex.

Usage:

twemoji.regex = /[\p{RGI_Emoji}--💩]/gv // set to match all RGI emojis, except for poop emoji
twemoji.parse('🦄💩') // only "🦄" is parsed
twemoji.regex = twemoji.defaultRegex // reset
twemoji.parse('🦄💩') // now both are parsed again

// here "ABC" is also parsed as an emoji
twemoji.parse(
    'ABC🦄💩',
    { regex: new RegExp(`ABC|${twemoji.defaultRegex.source}`, 'g') },
)

// to prevent any XSS risk, "<>&'\"" are skipped over,
// even if the user-supplied regex would match them
twemoji.parse('<>&\'"!', { regex: /[<>&'"!]/g }) // only "!" is parsed