a few places where help and manual are out of sync

[JeffBezanson]

Here are some examples. @threadcall has a docstring and ? works at the command line, but the macro doesn't seem to appear anywhere in the manual. Going the other way, exported constants like OS_NAME appear in the manual but ?OS_NAME says no documentation is found.

[tkelman]

ref #14264 (comment)

[kshyatt]

OS_NAME is deprecated now, but @threadcall still isn't in the manual afaict.

[vtjnash]

afaik, @threadcall is not in the manual because it is unsupported

[kshyatt]

Ok, will close this then. Reopen if needed.

[tkelman]

If it's unsupported we shouldn't have it at all. It's exported, so it should be documented. Or we should deprecate it.

[vtjnash]

I think that's @StefanKarpinski's call, since he wrote the implementation

[amitmurthy]

Mark it as experimental and document it?

[StefanKarpinski]

@amitmurthy's suggestion seems like the soundest one. Marking as 0.5.x.