std.typecons.wrap support for struct

[Jesse Phillips via Digitalmars-d]

Hey D peoples,

I just wanted to bring attention to a pull request I submitted. 
It adds the ability to use wrap and unwrap with a struct. It has 
had some review and I made updates. I realize there are bigger 
fish to fry but maybe there are some out there compiling their 
own compiler and would like to include this change and test.

https://github.com/D-Programming-Language/phobos/pull/2945