prepare_path: Directory creation and file path concatenation
Description
Given a folder, file base name and suffix, ensures the
directory exists, and returns the ready file path.
Usage
prepare_path(folder, fileBaseName, fileSuffix)
Arguments
folder
Folder path, without trailing slash
fileBaseName
File base name, excluding trailing dot
fileSuffix
File suffix without leading dot (e.g., "png", "pdf")