Add ability to process metadata

README.md

@@ -78,6 +78,7 @@ $response =
             ->setCallbackUrl('http://michaelakanji.com') // to override/set callback_url, it can also be set on your dashboard 
             ->setEmail( 'matscode@gmail.com' )
             ->setAmount( 75000 ) // amount is treated in Naira while using this method
+            ->setMetadata(['custom_field1' => 'value1', 'custom_field2' => 'value2'])
             ->initialize();
 ```
 If you want to get the 200OK raw Object as it is sent by Paystack, Set the 2nd argument of the `initialize()` to `true`, example below

src/Transaction.php

@@ -22,6 +22,7 @@ class Transaction extends Base
 			$amount = 0,
 			$email = null,
 			$reference = null,
+			$metadata = null,
 			$transactionResponse =
 			[
 				'verify'     => null,
@@ -82,6 +83,12 @@ public function initialize( array $data = [], $rawResponse = false )
 				$this->email = $data['email'];
 			}
 
+
+			// add metadata if provided
+			if ( ! is_null( $this->metadata ) ) {
+				$data['metadata'] = $this->metadata;
+			}
+
 			$this->transactionResponse['initialize'] =
 				$this
 					->setAction( 'initialize' )
@@ -284,4 +291,19 @@ public function setCallbackUrl( $callbackUrl )
 			return $this;
 		}
 
-	}
+
+				/**
+		 * Sets the metadata
+		 *
+		 * @param array $metadata
+		 *
+		 * @return $this
+		 */
+		public function setMetadata( $metadata )
+		{
+			$this->metadata = $metadata;
+
+			return $this;
+		}
+
+	}