Support ALIAS records with Cloudflare (#89)

* simple facility for registering provider capabilities

* support for cloudflare. tests.

* js and docs

* docs

* generate

docs/_functions/domain/ALIAS.md

@@ -0,0 +1,25 @@
+---
+name: ALIAS
+parameters:
+  - name
+  - target
+  - modifiers...
+---
+
+ALIAS is a virtual record type that points a record at another record. It is analagous to a CNAME, but is usually resolved at request-time and served as an A record. Unlike CNAMEs, ALIAS records can be used at the zone apex (`@`)
+
+Different providers handle ALIAS records differently, and many do not support it at all. Attempting to use ALIAS records with a DNS provider type that does not support them will result in an error.
+
+The name should be the relative label for the domain.
+
+Target should be a string representing the target. If it is a single label we will assume it is a relative name on the current domain. If it contains *any* dots, it should be a fully qualified domain name, ending with a `.`.
+
+{% include startExample.html %}
+{% highlight js %}
+
+D("example.com", REGISTRAR, DnsProvider("CLOUDFLARE"),
+  ALIAS("@", "google.com."), // example.com -> google.com
+);
+
+{%endhighlight%}
+{% include endExample.html %}