moved postman into separate crate

Cargo.toml

@@ -28,6 +28,9 @@ base64 = "0.13.0"
 [dependencies.regex_command_attr]
 path = "command_attributes"
 
+[dependencies.postman]
+path = "postman"
+
 [dependencies.serenity]
 git = "https://github.com/serenity-rs/serenity"
 branch = "next"