provides configuration directory for applications

 Many modules or applications maintain a user-spec configuration data
 directory. And the implementation pattern is generally the same.
 .
 A directory like /home/myuser/.application is created and populating by a set
 of default files the first time an application runs, and from there on, the
 files in that directory are modified.
 .
 File::UserConfig provides standard, light and sub-classable default
 implementation of this concept that Does The Right Thing with the directory
 names.