Added mailgun api client

mailgun/mailgun-php/2.3/config/packages/mailgun.yaml

@@ -0,0 +1,4 @@
+services:
+    Mailgun\Mailgun:
+        factory: ['Mailgun\Mailgun', create]
+        arguments: ['%env(MAILGUN_API_KEY)%']

mailgun/mailgun-php/2.3/manifest.json

@@ -0,0 +1,10 @@
+{
+    "copy-from-recipe": {
+        "config/": "%CONFIG_DIR%/"
+    },
+    "aliases": ["mailgun"],
+    "env": {
+        "#1": "Get your API key form https://app.mailgun.com/app/domains",
+        "MAILGUN_API_KEY": "\"replace_me\""
+    }
+}