Review a Committee Paper: exception_list

I will bring a draft of a committee paper I'm working on proposing an expanded, immutable exception_list class based on the exception_list class in the Parallelism TS. We'll informally discuss it as a group and have a discussion about it, with the intention of providing me and the other authors with some feedback.

The exception_list class in the Parallelism TS is a container-like exception class which can contain multiple exception_ptrs; the version in the Parallelism TS specifies a query interface, but provides no way for users to construct their own exception_lists.

The Parallelism TS has been voted into the C++17 working draft (including exception_list), but at Jacksonville there was some desire to expand the exception_list into a construct that can be used by C++ programmers.

This is one of our informal meetings, so if you have something that you'd like to discuss with the group, come to the meeting and let us know!

-- Bryce