The namespace::clean is a Perl pragma for keeping imported functions out of the current
namespace. This is especially important because Perl functions are naturally available
as methods, which can complicate subclassing. Using the namespace::clean pragma will
remove all previously declared or imported symbols at the end of the current package's
compile cycle. This means that functions called in the package itself will still be
bound by their name, but they won't show up as methods on your class or instances.
