Add: [AzurePipeline] introducing a release pipeline

This release pipeline creates all the official release binaries,
and publishes them as artifacts. Currently it can only produce
nightlies and custom builds; stable/testing release binaries are
untested.

This commit also splits up the pipeline in small bits, to both
improve readability, and to share code with the CI pipeline where
possible.

azure-pipelines/changelog.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+tag=$(git describe --tags 2>/dev/null)
+
+# If we are a tag, show the part of the changelog that matches the tag.
+# In case of a stable, also show all betas and RCs.
+if [ -n "$tag" ]; then
+    grep="."
+    if [ "$(echo $tag | grep '-')" = "" ]; then
+            grep='^[0-9]\.[0-9]\.[0-9][^-]'
+    fi
+    next=$(cat changelog.txt | grep '^[0-9]' | awk 'BEGIN { show="false" } // { if (show=="true") print $0; if ($1=="'$tag'") show="true"} ' | grep "$grep" | head -n1 | sed 's/ .*//')
+    cat changelog.txt | awk 'BEGIN { show="false" } /^[0-9].[0-9].[0-9]/ { if ($1=="'$next'") show="false"; if ($1=="'$tag'") show="true";} // { if (show=="true") print $0 }'
+    exit 0
+fi
+
+# In all other cases, show the git log of the last 7 days
+revdate=$(git log -1 --pretty=format:"%ci")
+last_week=$(date -u -d "$revdate -7days" +"%Y-%m-%d %H:%M")
+git log --after="${last_week}" --pretty=fuller