add target changelog which turns a package.xml into markdown

Makefile

@@ -67,4 +67,31 @@ doc:
 apidoc:
 	tools/apigen/bin/apigen SeedDMS_Core/Core --exclude "tests/*" --output html
 
-.PHONY: doc webdav webapp repository
+# Turn the package.xml file into CHANGELOG.md
+#
+# The idea is to form blocks of lines separated by an empty line.
+# Echo block consists of the version number, release date und notes.
+# This blocks are turned into single lines which are than sorted.
+# Afterwards the single lines are turned back into blocks.
+#
+# It first uses sgrep to extract the version, date und notes. This is
+# feed to sed to isolated the date and version and put them on separate
+# lines. Each version
+# forms a block of n lines with the first two being the version and date.
+# All remaining lines are notes. Blocks are separated by an empty line.
+# It's important to form blocks without ane empty lines because the following
+# awk will create a single line from each block which can then be sorted
+# (or simply reversed in order).
+# Because the blocks are listed in the wrong order (last version first and
+# previous version last, e.g. 5.1.29, 3.3.0, 3.3.1, ...., 5.1.27, 5.1.28) they
+# need to be reversed in order. This is done by turning each block into line
+# with the former new lines replaced by a '|'. So it's basically a '|' separated
+# csv file which is then reversed in order by 'sort -r'. In order to separate
+# blocks by a newline, each line of that output is appended by another
+# line break. Result is put back
+# into the original format by replacing all '|' by newline.
+#
+changelog:
+	@sgrep 'stag("DATE") .. etag("DATE") or ((stag("RELEASE") .. etag("RELEASE")) in (stag("VERSION") .. etag("VERSION"))) or inner(stag("NOTES") __ etag("NOTES"))' SeedDMS_Core/package.xml | sed -e 's#^ *<date>\([-0-9]*\)</date><release>\([0-9.]*\)</release>#\n\n\2 (\1)\n---------------------#' | awk -F'\n' -vRS='' -vOFS='|' '{$$1=$$1}1' | sort -V -r | sed 's/$$/\n/' | tr '|' '\n'
+
+.PHONY: doc webdav webapp repository changelog