Add SoftLayer DNS provider (#59)

Add SoftLayer DNS as a DomainServiceProvider.

The SoftLayer API is a bit of a mess and treats MX and SRV records
differently. This leads to some replication and custom handling issues
to work around.

In this patch I have to change the SRV test case to be _tcp instead of
_protocol because softlayer requires a "known" protocol which AFAICT is
tcp, udp or tls. I think this will be acceptable in most cases.

Signed-off-by: Jamie Lennox <jamielennox@gmail.com>

vendor/github.com/renier/xmlrpc/xmlrpc.go

@@ -0,0 +1,28 @@
+package xmlrpc
+
+import (
+	"fmt"
+)
+
+// xmlrpcError represents errors returned on xmlrpc request.
+type XmlRpcError struct {
+	Code           interface{}
+	Err            string
+	HttpStatusCode int
+}
+
+// Error() method implements Error interface
+func (e *XmlRpcError) Error() string {
+	return fmt.Sprintf(
+		"error: %s, code: %v, http status code: %d",
+		e.Err, e.Code, e.HttpStatusCode)
+}
+
+// Base64 represents value in base64 encoding
+type Base64 string
+
+type Params struct {
+	Params []interface{}
+}
+
+type Struct map[string]interface{}