[FEATURE] Add support for including directories

[battlesquid]

Description of the requested feature

Currently we can use the include directive to include an external yuck file, but it would be nice if we could include an entire directory. eww would look at the directory and include all present yuck files. This would be beneficial for organization if you have several reusable widgets/groups of widgets defined in separate files.

Proposed configuration syntax

The regular include directive would be used, the only difference is that the path would be allowed to point to a directory.

(include "/path/to/directory")

Additional context

No response