more filesystem predicates

Adds directory_files/2, file_exists/1, directory_exists/1.

Removed between/3, it's in the official package now.

v0.0.3

Updates ichiban/prolog to latest version.

v0.0.2

• dynamodb: Add attribute_value/2

v0.0.1

Includes:

• between/3
• consult/1 using io/fs
• DynamoDB client prototype (list_tables/1, scan/2, get_item/3, more to come).