Globbing: support for recursive directory matching `(**)`

[dregre]

Use of ** does not seem to work.

Example directory structure:

/a/b/c/foo.json
/a/b/c/bar.json
/a/b/xyz.json

My expectation is for the use of (fs/glob "**/*.json") to return a list containing three files, representing foo.json, bar.json, and xyz.json.

Instead, I get nil.

Doing (fs/glob (absolute "/a") "**/*.json") results in the same.

For expected behavior, see, e.g., glob behavior on Ruby.