add helper script to tag release

Cargo.toml

@@ -11,6 +11,7 @@ homepage = "https://hllmn.net/projects/jotdown"
 repository = "https://github.com/hellux/jotdown"
 documentation = "https://docs.rs/jotdown"
 exclude = [
+    "contrib",
     ".github",
     ".gitmodules",
     "Makefile",

contrib/tag-release.sh

@@ -0,0 +1,13 @@
+c_awk_latest='
+/^## \[.*\]/ {if (latest) exit; else {latest=1; next}}
+latest {print}
+'
+
+tag=$(grep ^version Cargo.toml | cut -d" " -f3 | tr -d '"')
+changes=$(awk "$c_awk_latest" CHANGELOG.md | tail -n+2)
+
+git -c core.commentchar='%' tag --edit \
+    -m "Release $tag" \
+    -m "$changes" \
+    "$tag"
+git push github master "$tag"