Add support for splitting all images in a directory

[raymondytian]

Description

This pull request allows users to specify a directory containing images to split. Additionally, it adds the option for recursive search through the entire directory tree to find images.

Changes Made

• Modified the image (now images) argument to accept a single image or a directory.
• Added a new flag argument -R or --recursive to enable recursive search for images in the directory.
• Implemented logic to recursively search through the directory tree if the -R flag is provided.

Example Usage

# Split all images in the specified directory (including subdirectories)
splix --images ~/Downloads -r 1,2,1 -c 2,1,2 -R