Source of RapidJSON

Indigo (at least as of 483e3e6b9afe2199faaab8d5ae5c3f5bf2a4a989) embeds a third party source of RapidJSON v1.1.0 under `third_party/rapidjson/`. However, the embedded code seems to differ from [RapidJSON's upstream](https://github.com/Tencent/rapidjson). Was there a different source for RapidJSON used, or were additional modifications of its code applied?

I am looking into updating Indigo in official Debian repositories. In Debian embedded source copies are reduced to minimum wherever possible. Building Indigo with `BUILD_STANDALONE=OFF` very nicely finds all the system-installed dependencies, however build fails due to RapidJSON incompatibility.