add utility for extracting name parts.

add API function for splitting up an item identifier into its mod name
and item name parts.

mods/bg_api/util_string.lua

@@ -21,3 +21,21 @@ end
 function blockgame.starts_with (str, start)
 	return string.sub(str, 1, string.len(start)) == start
 end
+
+
+
+function blockgame.extract_id_parts (name)
+	local basename
+	local modname
+
+	local colon_pos = string.find(name, ":")
+	if colon_pos then
+		modname = string.sub(name, 1, colon_pos - 1)
+		basename = string.sub(name, colon_pos + 1)
+	else
+		modname = minetest.get_current_modname()
+		basename = name
+	end
+
+	return basename, modname, modname .. ":" .. basename
+end