Comment parsing: improve the fidelity of XML output for many block commands

This change introduces a 'kind' attribute for the <Para> tag, that captures the
kind of the parent block command.

For example:

\todo Meow.

used to be just <Para>Meow.</Para>, but now it is
<Para kind="todo">Meow.</Para>


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174216 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed