Make the jupyterlite_contents glob recursive.

Since we have shifted to using globs for the contents, we might as well
enable the strictly more powerful ** recursive syntax. See https://docs.python.org/3/library/glob.html#glob.glob

"If recursive is true, the pattern “**” will match any files and zero or more directories, subdirectories and symbolic links to directories. If the pattern is followed by an os.sep or os.altsep then files will not match."

Author: jasongrout

jupyterlite_sphinx/jupyterlite_sphinx.py

@@ -300,7 +300,7 @@ def jupyterlite_build(app: Sphinx, error):
             jupyterlite_contents = [
                 match
                 for pattern in jupyterlite_contents
-                for match in glob.glob(pattern)
+                for match in glob.glob(pattern, recursive=True)
             ]
         jupyterlite_dir = app.env.config.jupyterlite_dir