Support JSON front matter as used by the Hugo site generator (fixes #270).

test/front-matter-alt-title-json.json

@@ -0,0 +1,6 @@
+{
+  "default": true,
+  "MD041": {
+    "front_matter_title": "^\\s*\"alternate\"\\s*:"
+  }
+}

test/front-matter-alt-title-json.md

@@ -0,0 +1,6 @@
+{
+"date": "2017-01-26T22:17:00+02:00",
+"alternate": "My document title and heading"
+}
+
+Some plain text here.

test/front-matter-title-json-spaces.json

@@ -0,0 +1,4 @@
+{
+  "default": true,
+  "MD041": true
+}

test/front-matter-title-json-spaces.md

@@ -0,0 +1,6 @@
+{
+"date": "2017-01-26T22:17:00+02:00",
+"title": "My document title and heading"
+}   
+
+Some plain text here.

test/front-matter-title-json.json

@@ -0,0 +1,4 @@
+{
+  "default": true,
+  "MD041": true
+}

test/front-matter-title-json.md

@@ -0,0 +1,6 @@
+{
+"date": "2017-01-26T22:17:00+02:00",
+"title": "My document title and heading"
+}
+
+Some plain text here.

test/hugo-quickstart-example-json.json

@@ -0,0 +1,4 @@
+{
+  "default": true,
+  "MD041": true
+}

test/hugo-quickstart-example-json.md

@@ -0,0 +1,13 @@
+{
+    "title": "Another Hugo Post",
+    "description": "Nothing special, but one post is boring.",
+    "date": "2014-09-02",
+    "categories": [ "example", "configuration" ],
+    "tags": [
+        "example",
+        "hugo",
+        "toml"
+    ],
+}
+
+# Heading {MD025}