dev-R/lattice: fix and improve src_uri, add optfeature for dev-R/MASS

* Improve SRC_URI to use ver_rs and not a hard coded URI
* Add optfeature for dev-R/MASS

Currently, dev-R/lattice will not fetch because the source for
version 0.20.44 has been archived. Therefore, the package must use
the URL for archived versions. In addition, the ver_rs function is used
because the URI for the package replaced the second period with a '-'
in the version number. Since https://cran.r-project.org/ is listed in
thirdpartymirrors, it should be referenced in SRC_URI with a mirror:///
URI. In addition, dev-R/MASS will enable optional features so an
optfeature function is added. Also, the HOMEPAGE variable was set.

Closes: https://bugs.gentoo.org/815781
Package-Manager: Portage-3.0.20, Repoman-3.0.3
Signed-off-by: Lucas Mitrak <lucas@lucasmitrak.com>

dev-R/lattice/lattice-0.20.44.ebuild

@@ -3,11 +3,12 @@
 
 EAPI=7
 
-inherit R-packages
+inherit R-packages optfeature
 
 DESCRIPTION='Trellis Graphics for R'
+HOMEPAGE="http://lattice.r-forge.r-project.org/index.php"
 KEYWORDS="~amd64"
-SRC_URI="http://cran.r-project.org/src/contrib/lattice_0.20-44.tar.gz"
+SRC_URI="mirror://cran/src/contrib/Archive/"{$PN}"/"${PN}"_"$(ver_rs 2 '-')".tar.gz -> "${P}".tar.gz"
 LICENSE='GPL-2+'
 
 DEPEND="
@@ -15,3 +16,7 @@ DEPEND="
 	dev-lang/R[minimal]
 "
 RDEPEND="${DEPEND}"
+
+pkg_postinst() {
+	optfeature "immer in the MASS package for data from the same experiment (expressed as total yield for 3 blocks) for a subset of varieties" dev-R/MASS
+}