Add undef-init rule (with yo eslint:rule) and tests for it

docs/rules/undef-init.md

@@ -0,0 +1,36 @@
+# Always initialize variables during declaration. Set it explicitly to undefined, if required. (undef-init)
+
+Please describe the origin of the rule here.
+
+
+## Rule Details
+
+This rule aims to...
+
+Examples of **incorrect** code for this rule:
+
+```js
+
+// fill me in
+
+```
+
+Examples of **correct** code for this rule:
+
+```js
+
+// fill me in
+
+```
+
+### Options
+
+If there are any options, describe them here. Otherwise, delete this section.
+
+## When Not To Use It
+
+Give a short description of when it would be appropriate to turn off this rule.
+
+## Further Reading
+
+If there are other links that describe the issue this rule addresses, please include them here in a bulleted list.