Allow options for writing and parsing NaN/Infinity

[m7thon]

This adds kWriteNanAndInfFlag to Writer to allow writing of nan,
inf and -inf doubles as "NaN", "Infinity" and "-Infinity",
respectively, and kParseNanAndInfFlag to Reader to allow parsing
of "NaN", "Inf", "Infinity", "-Inf" and "-Infinity". This is part
of issue #36, adding optional support for relaxed JSON syntax.

[coveralls]

Coverage decreased (-0.04%) to 99.958% when pulling 6dd76fb on m7thon:allow_nan_and_inf into 2a3fbda on miloyip:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 135da7a on m7thon:allow_nan_and_inf into 2a3fbda on miloyip:master.

[miloyip]

Thank you

[qywx]

How to use this with FileReadStream is and doc.ParseStream(is)

rj::Document doc;
auto filepath = "ncd.json";
FILE* fp = fopen(filepath, "rb");
std::vector<char> buf(262144);
rj::FileReadStream is(fp, buf.data(), buf.capacity());
doc.ParseStream(is);  // after this buffer may/could be reused or deleted.
fclose(fp);

?

Update. I found a way:

doc.ParseStream<rj::kParseNanAndInfFlag>(is);  // after this buffer may/could be reused or deleted.

it was not obvious.
But I still get an assert failed IsNumber() when GetDouble() of rj::Value which is "NaN".

Update 2. SOLVED. NaN must be without quotes.

Thanks to authors.

[xiaoxiangdu]

Hello, can we support more NaNs, such nan,Nan etc?

[xiaoxiangdu]

And infinity, inf etc?