Add script to help in generating release changelog

pr2relnotes.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env sh
+
+if [ -z $1 ]
+then
+    echo "pr2relnotes.sh: prints list of pull requests merged since <tag>"
+    echo "  usage: $0 <tag> [pull-request-url (default: https://github.com/erlware/relx/pull/)]"
+    exit 0
+fi
+export url=${2:-"https://github.com/erlware/relx/pull/"}
+
+git log --merges --pretty=medium $1..HEAD | \
+awk -v url=$url '
+    # first line of a merge commit entry
+    /^commit / {mode="new"}
+
+    # merge commit default message
+    / +Merge pull request/ {
+        page_id=substr($4, 2, length($4)-1);
+        mode="started";
+        next;
+    }
+
+    # line of content including title
+    mode=="started" && /    [^ ]+/ {
+        print "- [" substr($0, 5) "](" url page_id ")"; mode="done"
+    }'