[clang-tidy] Move clang-tidy docs to a separate directory. Create doc files for checks

The doc files for checks have been generated from the corresponding header files
using the docs/clang-tidy/tools/dump_check_docs.py script. Committing the script
as well, but the intention is to move all the user-facing docs from header files
to the rST files and add links to .h files appropriately.

llvm-svn: 246173
diff --git a/clang-tools-extra/docs/Doxyfile b/clang-tools-extra/docs/Doxyfile
index c216f42..d674390 100644
--- a/clang-tools-extra/docs/Doxyfile
+++ b/clang-tools-extra/docs/Doxyfile
@@ -648,7 +648,7 @@
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = ../clang-modernize ../clang-apply-replacements
+INPUT                  = ../clang-modernize ../clang-apply-replacements ../clang-tidy
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is