Add MD034 with tests, improve validation of README and Rules.

lib/rules.js

@@ -619,5 +619,32 @@ module.exports = [
           errors.push(token.lineNumber);
         });
     }
+  },
+
+  {
+    "name": "MD034",
+    "desc": "Bare URL used",
+    "tags": [ "links", "url" ],
+    "func": function MD034(params, errors) {
+      filterTokens(params.tokens, "inline")
+        .forEach(function forToken(token) {
+          var lineNumber = token.lineNumber;
+          var inLink = false;
+          token.children.forEach(function forChild(child) {
+            if (child.type === "link_open") {
+              inLink = true;
+            } else if (child.type === "link_close") {
+              inLink = false;
+            } else if ((child.type === "text") &&
+                       !inLink &&
+                       /https?:\/\//.test(child.content)) {
+              errors.push(lineNumber);
+            } else if ((child.type === "softbreak") ||
+                       (child.type === "hardbreak")) {
+              lineNumber++;
+            }
+          });
+        });
+    }
   }
 ];