Add _incr_version to contrib/

contrib/_incr_version

@@ -0,0 +1,33 @@
+#!/bin/sh -eu
+old_version="$1"
+new_version="$2"
+sed -i meson.build -e "s/version: '$old_version'/version: '$new_version'/g"
+
+printf "Backwards-incompatible ABI changes? (y/n) "
+read inc_age
+if [ "$inc_age" = 'n' ]
+then
+	printf "Interface(s) added, removed, or changed? (y/n) "
+	read inc_current
+fi
+
+so_version=$(egrep '^so_version =' meson.build | cut -d'[' -f2- | cut -d']' -f1)
+current=$(echo "$so_version" | cut -d',' -f1 | sed -e "s/'//g" -e "s/ //g")
+revision=$(echo "$so_version" | cut -d',' -f2 | sed -e "s/'//g" -e "s/ //g")
+age=$(echo "$so_version" | cut -d',' -f3 | sed -e "s/'//g" -e "s/ //g")
+
+if [ "$inc_age" = 'y' ]
+then
+	age=$((age+1))
+	current=$((current+1))
+elif [ "$inc_current" = 'y' ]
+then
+	current=$((current+1))
+fi
+revision=$((revision+1))
+
+sed -i meson.build \
+	-e "s/so_version = .*/so_version = ['$current', '$revision', '$age']/g"
+
+git add meson.build
+git commit -m "Update version to $new_version"