libsodium: Update to 1.0.18-20200728

It has been over a year since the 1.0.18 release, but the project
recommends using the stable branch which has further fixes. Rework the
Portfile to accommodate this.

The github portgroup livecheck tells you if the latest commit hash is
different. A custom livecheck on my server tells you the latest version
and date by checking the releases directory on their server. I wasn't
sure which one of these was more useful so I've left both in the
Portfile with the former activated for now.

Closes: https://trac.macports.org/ticket/48579

devel/libsodium/Portfile

@@ -3,9 +3,15 @@
 PortSystem          1.0
 PortGroup           github 1.0
 PortGroup           muniversal 1.0
-PortGroup           cxx11 1.1
 
-github.setup        jedisct1 libsodium 1.0.18-RELEASE
+# Upstream recommends using the stable branch:
+# https://doc.libsodium.org/installation
+github.setup        jedisct1 libsodium d37afd6015fa246b967aa216611874883e5670c1
+version             1.0.18-20200728
+revision            0
+checksums           rmd160  154e61138bc9e14f6823caed62c3841b5fb180e0 \
+                    sha256  b9d55bdc55bf4bbea83c614558a5a3dd0af1cec7fd1d0e2a6081a77064a086c3 \
+                    size    2041012
 
 categories          devel security
 platforms           darwin
@@ -18,14 +24,23 @@ description         Portable and packageable NaCl-based crypto library
 long_description    libsodium is a library for network communication, \
                     encryption, decryption, signatures, etc.
 
-checksums           rmd160  48941eaf00afe9061796a4753ed320e81a8be95e \
-                    sha256  34f0c6a2c05ea5e5968d2231f2fd2ea35c29b8d9119045563deb64e680c7da99 \
-                    size    2046708
+github.tarball_from archive
 
 depends_build-append \
                     port:pkgconfig
 
+compiler.cxx_standard \
+                    2011
+
 configure.args      --disable-silent-rules
 
 test.run            yes
 test.target         check
+
+github.livecheck.branch \
+                    stable
+
+#livecheck.type      regex
+#livecheck.version   ${version}
+#livecheck.url       http://www.ryandesign.com/macports/version.php/${name}
+#livecheck.regex     {^([^-]+-\d{8})}