Make the Token arg of buildSignature() methods optional.

RSA-SHA1 buildSignature() doesn't use it at all, and the other two allow for there to be no token, as on the initial client request. The token shared-secret as taken to be an empty string.

src/GaryJones/OAuth/HmacSha1.php

@@ -52,7 +52,7 @@ class HmacSha1 extends SignatureMethod
      *
      * @return string
      */
-    public function buildSignature(Request $request, Client $client, Token $token)
+    public function buildSignature(Request $request, Client $client, Token $token = null)
     {
         $base_string = $request->getSignatureBaseString();
         $request->base_string = $base_string;

src/GaryJones/OAuth/PlainText.php

@@ -50,7 +50,7 @@ class PlainText extends SignatureMethod
      *
      * @return string
      */
-    public function buildSignature(Request $request, Client $client, Token $token)
+    public function buildSignature(Request $request, Client $client, Token $token = null)
     {
         $key_parts = array(
             $client->getSecret(),

src/GaryJones/OAuth/RsaSha1.php

@@ -33,7 +33,7 @@ abstract class RsaSha1 extends SignatureMethod
      */
     public function getName()
     {
-        return "RSA-SHA1";
+        return 'RSA-SHA1';
     }
 
     /**
@@ -64,7 +64,7 @@ abstract class RsaSha1 extends SignatureMethod
      *
      * @return string
      */
-    public function buildSignature(Request $request, Client $client, Token $token)
+    public function buildSignature(Request $request, Client $client, Token $token = null)
     {
         $base_string = $request->getSignatureBaseString();
         //$request->base_string = $base_string;

src/GaryJones/OAuth/SignatureMethod.php

@@ -42,7 +42,7 @@ abstract class SignatureMethod
      *
      * @return string
      */
-    abstract public function buildSignature(Request $request, Client $client, Token $token);
+    abstract public function buildSignature(Request $request, Client $client, Token $token = null);
 
     /**
      * Verifies that a given signature is correct.