Update the coding standards, removign the bit about avoiding exceptions and

Update the coding standards, removign the bit about avoiding exceptions and
rtti (they shouldn't be used in the main compiler, but that's because
optimizations aren't allowed to fail!)

Remove the big section about iterators, because people who do not know what
they are doing shouldn't be writing them.  :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13670 91177308-0d34-0410-b5e6-96231b3b80d8