cpp docs

Hey we have to look into this:

https://staging.haxe.org/manual/target-cpp.html

* [ ] [The overview](https://staging.haxe.org/manual/target-cpp.html) doesn't list the new docs
* [ ] The subpages don't have the section number, but they seem to use the first word (sometimes without the last letter).
* [ ] https://staging.haxe.org/manual/hxcpp/docs/build_xml/Defines.html table layout is pretty messed up :o
* [ ] https://staging.haxe.org/manual/hxcpp/docs/build_xml/Compiler.html backticks are not correct processed here
* [ ] https://staging.haxe.org/manual/hxcpp/docs/build_xml/Linker.html Has lot of extra backticks around inline code elements.

Maybe the last 3 points can be a matter of changing the markdown in the original docs?