Add documentation for clang-format.

This adds documentation for both LibFormat as well as the standalone
tools and integrations built on top of it. It slightly restructures
the ClangTools documentation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172004 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the unused Parser::ParseTranslationUnit function

Parser::ParseTranslationUnit is now dead because the loop over
ParseTopLevelDecl is in ParseAST.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172005 91177308-0d34-0410-b5e6-96231b3b80d8