Add markdown preview, update rust.vim

sources_non_forked/markdown-preview.nvim/tslint.json

@@ -0,0 +1,22 @@
+{
+  "extends": ["tslint:latest", "tslint-config-prettier"],
+  "rulesDirectory": ["tslint-plugin-prettier"],
+  "rules": {
+    "prettier": [
+      true,
+      {
+        "semi": false,
+        "singleQuote": true
+      }
+    ],
+    "no-submodule-imports": false,
+    "object-literal-sort-keys": false
+  },
+  "linterOptions": {
+    "exclude": [
+      "./lib/",
+      "./node_modules"
+    ]
+  }
+}
+