whitespace must precede closing comment token

[billh0420]

I believe whitespace must precede the closing comment token.

The current version does the following:

 $( something $)$) yields " something $)"

 $( something junk$) yields " something junk"

 $( something $)junk$) yields " something $)junk"

 $( something ($) more $) yields error

The first three examples should continue looking for closing comment token.

The last example should yield " something ($) more "

[billh0420]

Note: lines 97-107 might be clearer if written as:

if text->Js.String2.charAt(foundIdx - 1)->isWhitespace == false { // need leading whitespace
    setIdx(foundIdx+1)
}
else if !(endOfFile.contents || ch.contents->isWhitespace) { // need trailing whitespace or endOfFile
    setIdx(foundIdx+1)
}
else {
    result.contents = Some(Some(text->Js_string2.substring(~from=beginIdx, ~to_=foundIdx)))
    setIdx(foundIdx + 2)
}

This avoids advancing idx by 2 always and then moving idx back by 1 in the two exceptional cases.

I didn't test this new code: not sure if you even want it.

Would you prefer I make the change and test it?

[expln]

Thanks for submitting this PR. I compared how metamath-exe processes comments vs mm-lamp. Unfortunately, it appeared to be not so easy task. When I put $( something ($) more $) somewhere in the middle of an *.mm file, metamath-exe failed to parse such a file, similarly mm-lamp fails. Ideally I want mm-lamp to behave the same way as metamath-exe does. Currently they seem to behave similarly in terms of parsing comments. But according to the Metamath book, the end of a comment indeed should be preceded by a whitespace (Appendix E, Metamath Language EBNF). This could be a bug in metamath-exe too. I need more time to analyze this situation.