Add script to publish stubs subspit [skip ci]

Author: pinepain

scripts/subsplit.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )"
+
+cd $DIR
+
+if [ -d ".subsplit" ]; then
+    git subsplit update
+else
+    git subsplit init .
+fi
+
+git subsplit publish --heads="master" stubs:git@github.com:pinepain/php-v8-stubs.git