Storage get enhanced

[knyipab]

This goal of this request is to enrich termux-storage-get to what "Open ..." and "Open Folder ..." usually do in PC, while keeping backward compatibility.

See the show_usage() below for more information.

• high backward compatibility (termux-storage-get output-name works as usual)
• print URIs in JSON array (or line format with -l)
• when output-name is not present, only print out URIs
• synchronous call (wait until finish)
• open folder
• persistable permission grant (persist after reboot)
• supprot to get multiple file (accompany with output-name patterns like %d, %8d, %08d)
• specify MIME type