Build normal and extended versions for the registry images

Closes pages/hugo#29

Dockerfile

@@ -1,15 +1,21 @@
 FROM alpine:latest
 
-ENV HUGO_VERSION 0.55.6
-ENV HUGO_SHA 39d3119cdb9ba5d6f1f1b43693e707937ce851791a2ea8d28003f49927c428f4
+ARG HUGO=hugo
+ARG HUGO_VERSION=0.55.6
+ARG HUGO_APK="ca-certificates openssl git"
+ARG HUGO_SHA=39d3119cdb9ba5d6f1f1b43693e707937ce851791a2ea8d28003f49927c428f4
+ARG HUGO_EXTENDED_APK="libc6-compat libstdc++"
+ARG HUGO_EXTENDED_SHA=8962b8cdc0ca220da97293cea0bb1b31718cb4d99d0766be6865cb976b1c1805
 
 # Install HUGO
 RUN set -eux && \
-    apk add --update --no-cache \
-      ca-certificates \
-      openssl \
-      git && \
-  wget -O ${HUGO_VERSION}.tar.gz https://github.com/spf13/hugo/releases/download/v${HUGO_VERSION}/hugo_${HUGO_VERSION}_Linux-64bit.tar.gz && \
+    case ${HUGO} in \
+      *_extended) \
+        HUGO_APK="${HUGO_APK} ${HUGO_EXTENDED_APK}" \
+        HUGO_SHA="${HUGO_EXTENDED_SHA}" ;; \
+    esac && \
+    apk add --update --no-cache ${HUGO_APK} && \
+  wget -O ${HUGO_VERSION}.tar.gz https://github.com/spf13/hugo/releases/download/v${HUGO_VERSION}/${HUGO}_${HUGO_VERSION}_Linux-64bit.tar.gz && \
   echo "${HUGO_SHA}  ${HUGO_VERSION}.tar.gz" | sha256sum -c && \
   tar xf ${HUGO_VERSION}.tar.gz && mv hugo* /usr/bin/hugo && \
   rm -rf  ${HUGO_VERSION}.tar.gz && \
@@ -18,4 +24,4 @@ RUN set -eux && \
 
 EXPOSE 1313
 
-CMD ["/usr/local/bin/hugo"]
+CMD ["/usr/bin/hugo"]