Documentation cleanup, fixing Doxygen markup. Mostly this avoids common terms
such as "protocol" and "expression" being implicitly turned into links to
mistakenly-generated Doxygen pages:
- Escaping @ symbols when Doxygen would otherwise incorrectly interpret them;
- Escaping # symbols when they're not intended as explicit Doxygen link 
  requests, such as when discussing preprocessor directives;
- In one odd case, unescaping @ in @__experimental_modules_import, because
  Doxygen wrote '\@' to the output in that case, causing the example in the
  description of ImportDecl to be wrong; and
- Fixing a typo: @breif -> @brief.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158299 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed