Add install step for dependencies

patch.php

@@ -0,0 +1,50 @@
+<?php
+
+// patch files for PHP 7.0 compatibility
+
+function patchDir(string $base, string $dir): int
+{
+    $count = 0;
+    $entries = scandir($dir);
+    foreach ($entries as $entry) {
+        if ($entry === '.' || $entry === '..') {
+            continue;
+        }
+        $filename = "$base/$dir/$entry";
+        if (is_dir($filename)) {
+            $count += patchDir($base, "$dir/$entry");
+        }
+    }
+    foreach ($entries as $entry) {
+        $filename = "$base/$dir/$entry";
+        if (is_file($filename)) {
+            if (substr($entry, -4) != '.php') {
+                continue;
+            }
+            $patched = $original = file_get_contents($filename);
+            $patched = preg_replace('/\):\s*(\?[a-zA-Z]+|void)\s*\n/', ") /*:$1*/\n", $patched);
+            $patched = preg_replace('/(private|public|protected) const/', "/*$1*/ const", $patched);
+            if ($patched && $patched != $original) {
+                file_put_contents($filename, $patched);
+                $count++;
+            }
+        }
+    }
+    return $count;
+}
+
+function patch(string $base, array $dirs)
+{
+    $start = microtime(true);
+    $count = 0;
+    foreach ($dirs as $dir) {
+        $count += patchDir($base, $dir);
+    }
+    $end = microtime(true);
+    $time = ($end - $start) * 1000;
+    if ($count) {
+        fwrite(STDERR, sprintf("%d files patched in %d ms\n", $count, $time));
+    }
+}
+
+patch(__DIR__, ['vendor']);