UTF8 library

-- Constants
utf8.charpattern: string

-- Methods
function utf8.offset(s: string, n: number, i: number?): number?
function utf8.codepoint(s: string, i: number?, j: number?): ...number
function utf8.char(...: number): string
function utf8.len(s: string, i: number?, j: number?): number?
function utf8.codes(s: string): ((string, number) -> (number, number), string, number) -- <iterator>