Update the py-pkg-deps.py example
Add example for displaying package categories
Add example for displaying options
Add __str__ method to PkgFile type
Add an example for displaying packag files
Add example for displaying package repositories
Add example for updating the package repositories.
Add example for displaying the required shared libraries by a package
Add a pkg_is_installed() method for testing if package is installed or not
Fix pkg_is_installed() method
Add example for checking the database for missing package dependencies