Fix string.find and string.match from unexpected explosions

[jordan4ibanez]

I was reading the documentation for string.find and I noticed that in it's own documentation it reads:

/**
  * Looks for the first match of pattern (see §6.4.1) in the string s. If it
  * finds a match, then find returns the indices of s where this occurrence
  * starts and ends; otherwise, it returns nil.
  * /

I see the definition defined as:

function find(
    s: string,
    pattern: string,
    init?: number,
    plain?: boolean
): LuaMultiReturn<[number, number, ...string[]] | []> ;

Perhaps the easiest solution for this would be to simply add optional return parameters as follows:

function find(
    s: string,
    pattern: string,
    init?: number,
    plain?: boolean
): LuaMultiReturn<[number?, number?, ...string[]] | []> ;

So this way, at least you know it might explode instead of blindly walking into an explosion.

Also:
I noticed that string.match could also blow up so I threw that in there.