* Fixes#1810
There's still a problem with stereo atoms (see the commented out test),
but this takes care of the basics and that's up next.
* clean up that last problematic bit.
Still needs all tests to run
* this seems to be a necessary workaround for problems with VS2017.
It's a bit ugly, but shouldn't have any performance impact, so I'm not
going to get too worked up.
* This set of changes alters what we get for some of the InChI test cases.
Adjust for that.
* boost::thread mostly gone... still need to get rid of once
everything compiles
* replace boost::call_once
* remove link-time dependency on boost::thread
* first pass at using async
* switch to using async everywhere
