Added CWG and SG1 papers to libc++ status page

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@188381 91177308-0d34-0410-b5e6-96231b3b80d8
remove CWG papers from list; add link to clang status page

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@188383 91177308-0d34-0410-b5e6-96231b3b80d8