Previously, `dyn_templates` walked the user-provided `template_dir` path by
constructing a glob pattern prefixed with `template_dir`. If `template_dir`
contained characters recognized by the glob pattern parser, then at best the
pattern failed to parse, and at worst, incorrect directories were searched.
This commit removes the use of `glob` to walk the templates directory and
instead uses `walkdir`, obviating the issues described above.
Fixes#2627.
Sergio Benitez