Documentation cleanup:

* Escaped @ symbols that shouldn't be interpreted by Doxygen;
* Deleted \param documentation for function parameters that no longer exist;
* Fixed parameter names in \param Doxygen commands;
* Fixed some broken formatting.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158505 91177308-0d34-0410-b5e6-96231b3b80d8