NEW PROVIDER: AutoDNS (#1336)

* Implement AutoDNS provider to manage existing zones

* Moved AuditRecords() in to separate file to ease automatic updating

* S1011 - Use a single append to concatenate two slices

* Set list of available record types as returned by the system

* Fixed style, clarify code and add some extra comments

* Documented simple configuration and usage example of AutoDNS

* Convert MX and SRV record properly from string to actual structs and back

* Add support for integration tests of AutoDNS

* Return error message from update request instead of invoking panic()

* Skip AUTODNS in test for RFC 7505 (null MX)

* Update providers/autodns/autoDnsProvider.go

Co-authored-by: Tom Limoncelli <tlimoncelli@stackoverflow.com>

docs/_providers/autodns.md

@@ -0,0 +1,35 @@
+---
+name: AutoDNS
+title: AutoDNS (InternetX)
+layout: default
+jsId: AUTODNS
+---
+
+# AutoDNS Provider
+
+## Configuration
+
+In your credentials file, you must provide [username, password and a context](https://help.internetx.com/display/APIXMLEN/Authentication#Authentication-AuthenticationviaCredentials(username/password/context)).
+
+{% highlight json %}
+{
+  "autodns": {
+    "username": "autodns.service-account@example.com",
+    "password": "[***]",
+    "context": "33004"
+  }
+}
+{% endhighlight %}
+
+## Usage
+
+Example Javascript:
+
+{% highlight js %}
+var REG_NONE = NewRegistrar('none', 'NONE');
+var HETZNER = NewDnsProvider("autodns", "AUTODNS");
+
+D("example.tld", REG_NONE, DnsProvider(AUTODNS),
+    A("test","1.2.3.4")
+);
+{%endhighlight%}