vlib: filepath module

vlib/os/os.v

@@ -4,7 +4,7 @@
 
 module os
 
-import strings
+import filepath
 
 #include <sys/stat.h>
 #include <signal.h>
@@ -920,13 +920,7 @@ pub fn mkdir_all(path string) {
 	}
 }
 
-// TODO use []string.join once ...string becomes "[]string"
 pub fn join(base string, dirs ...string) string {
-	mut path := strings.new_builder(50)
-	path.write(base.trim_right('\\/'))
-	for d in dirs {
-		path.write(os.path_separator)
-		path.write(d)
-	}
-	return path.str()
+	println('use filepath.join')
+	return filepath.join(base, dirs)
 }