CPAN apparently changed the by-authors download URL structures because
http://cpan.perl.org/modules/by-authors/id/$_author/

 does not work
anymore. The directory structure appears to be 'by-authors/id/<first
letter>/<first two letters>/$_author', which significantly reduces the
usefulness of _author in the default PKGBUILD.

I changed the source array to download by-module instead of by-author to
make things simple. The _author variable is no longer needed, and I
added a _modnamespace variable to handle CPAN's URL format.

Signed-off-by: Jason St. John <jstjohn@purdue.edu>