[clang-tidy] Update docs for clang-tidy checks. NFC

Changes mostly address formatting and unification of the style. Use
MarkDown style for inline code snippets and lists. Added some text
for a few checks.

The idea is to move most of the documentation out to separate rST files and have
implementation files refer to the corresponding documentation files.

llvm-svn: 246169
diff --git a/clang-tools-extra/clang-tidy/misc/MacroParenthesesCheck.cpp b/clang-tools-extra/clang-tidy/misc/MacroParenthesesCheck.cpp
index d1450b6..f617694 100644
--- a/clang-tools-extra/clang-tidy/misc/MacroParenthesesCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/MacroParenthesesCheck.cpp
@@ -54,14 +54,14 @@
 
 /// Is given TokenKind a keyword?
 static bool isKeyword(const Token &T) {
-  /// \TODO better matching of keywords to avoid false positives
+  // FIXME: better matching of keywords to avoid false positives.
   return T.isOneOf(tok::kw_case, tok::kw_const, tok::kw_struct);
 }
 
 /// Warning is written when one of these operators are not within parentheses.
 static bool isWarnOp(const Token &T) {
-  /// \TODO This is an initial list of operators. It can be tweaked later to
-  /// get more positives or perhaps avoid some false positive.
+  // FIXME: This is an initial list of operators. It can be tweaked later to
+  // get more positives or perhaps avoid some false positive.
   return T.isOneOf(tok::plus, tok::minus, tok::star, tok::slash, tok::percent,
                    tok::amp, tok::pipe, tok::caret);
 }