Update wren to 0.3.0

Upstream repo got wren-cli split out into a separate
git repo so it can't be built as part of the wren
repo anymore. Unit tests have also changed, meson
script now relies on a python find script to get all
the *.wren files that should be passed to the unit
test executable.

subprojects/wren/find_scripts.py

@@ -0,0 +1,12 @@
+#!/usr/bin/env python
+
+from pathlib import Path
+import sys
+
+if len(sys.argv) < 2:
+    sys.stderr.write("Please specify a search directory\n")
+    exit(2)
+
+for search_path in sys.argv[1:]:
+    for path in Path(search_path).rglob('*.wren'):
+        sys.stdout.write(str(path) + "\n")