remove all the random "include gentoo" and rename files as init.pp

For some reason puppet doesn't like them being named the same as the modules
we're referencing.

manifests/keywords.pp

 define gentoo::keywords ($source, $ensure=present) {
-    include gentoo
-
     file {
         "gentoo_keywords_${name}":
             path    => "/etc/portage/package.keywords/${name}",

manifests/mask.pp

 define gentoo::mask ($source="", $ensure=present) {
-    include gentoo
-
     file {
         "gentoo_mask_${name}":
             path    => "/etc/portage/package.mask/${name}",

manifests/unmask.pp

 define gentoo::unmask ($source, $ensure=present) {
-    include gentoo
     file {
         "gentoo_unmask_${name}":
             path    => "/etc/portage/package.unmask/${name}",

manifests/use.pp

 define gentoo::use ($source, $ensure=present) {
-    include gentoo
-
     file {
         "gentoo_use_${name}":
             path    => "/etc/portage/package.use/${name}",