emoji.lua: Add rofl=😂 and other improvements

    Linter: functions explicitly go to _G or are local
    Emoji table is now downloaded from a db
    str2emoji(): simplify pattern, gsub points to table instead of function (faster)
    use string.find in conditionals not string.match
    Use function alias for functions that all do the same thing
    tabs search last :token: and look/replace with approximations

Author: Nomarian