First version of this document. It is still missing some pretty big pieces, and

First version of this document.  It is still missing some pretty big pieces, and
the debugging information formats will likely change, but it's a start, and I
have to move on to other things in the short-term, so it might be a while before
I get back to working on this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10683 91177308-0d34-0410-b5e6-96231b3b80d8