Wrote README

Add new features
Fixed link to the ExifTool website and removed some other bad
Use of pragmas

strict
warnings
diagnostics
Some better text for labels lbl_details_file and lbl_details_tag
Added do_system_command function

Tags can be edit now.
Added functions to remove a specific tag or delete all metadata

on_metadata_remove_activate: removes a specific tag.
on_metadata_delete_activate: deletes all metadata.
Removed gobal variable $selection
Wrapped long lines
Set version to 0.0.2