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
diff --git a/docs/index.rst b/docs/index.rst
index 4a20bb9..66906e5 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -32,14 +32,24 @@
    Tooling
    IntroductionToTheClangAST
    LibTooling
+   LibFormat
    ClangPlugins
    RAVFrontendAction
    LibASTMatchersTutorial
    LibASTMatchers
-   ClangTools
    HowToSetupToolingForLLVM
    JSONCompilationDatabase
 
+Using Clang Tools
+=================
+
+.. toctree::
+   :maxdepth: 1
+
+   ClangTools
+   ClangCheck
+   ClangFormat
+
 Design Documents
 ================