new: Add gitchangelog template

.gitchangelogrst.tpl

+% if data["title"]:
+${data["title"]}
+\n
+${"=" * len(data["title"])}
+
+
+% endif
+% for version in data["versions"]:
+<%
+title = "%s (%s)" % (version["tag"], version["date"]) if version["tag"] else opts["unreleased_version_label"]
+
+nb_sections = len(version["sections"])
+%>${title}
+${"-" * len(title)}
+% for section in version["sections"]:
+% if not (section["label"] == "Other" and nb_sections == 1):
+
+${section["label"]}
+${"~" * len(section["label"])}
+% endif
+% for commit in section["commits"]:
+<%
+subject = "%s [%s]" % (commit["subject"], ", ".join(commit["authors"]))
+entry = indent('\n'.join(textwrap.wrap(subject)),
+                       first="- ").strip()
+%>${entry}
+
+% if commit["body"]:
+${indent(commit["body"])}
+% endif
+% endfor
+% endfor
+
+% endfor