Clean up remove caddy refs (#139)

* Changed reference to Caddy over to CoreDNS

* Removing references to caddy

* Fixed misleading error message to reference coredns

* Cleaning up references to caddy

* Adding clean and deps targets

Muscle memory is resulting in "make clean" commands.

* Adding test target to makefile

* More "Caddy" cleanup

core/directives.go

@@ -68,7 +68,7 @@ var directiveOrder = []directive{
 	{"proxy", setup.Proxy},
 }
 
-// RegisterDirective adds the given directive to caddy's list of directives.
+// RegisterDirective adds the given directive to CoreDNS's list of directives.
 // Pass the name of a directive you want it to be placed after,
 // otherwise it will be placed at the bottom of the stack.
 func RegisterDirective(name string, setup SetupFunc, after string) {