Add support and tests for tags, migrate style files.

style/all.json

@@ -1,3 +1,5 @@
 {
+  "comment": "All rules",
+
   "default": true
 }

style/cirosantilli.json

@@ -0,0 +1,18 @@
+{
+  "comment": "Rules for the style guide at http://www.cirosantilli.com/markdown-style-guide/",
+
+  "default": true,
+  "MD003": {
+    "style": "atx"
+  },
+  "MD004": {
+    "style": "dash"
+  },
+  "MD007": {
+    "indent": 4
+  },
+  "MD030": {
+    "ul_multi": 3,
+    "ol_multi": 2
+  }
+}

style/relaxed.json

@@ -0,0 +1,9 @@
+{
+  "comment": "Relaxed rules",
+
+  "default": true,
+  "whitespace": false,
+  "line_length": false,
+  "MD006": false,
+  "MD007": false
+}