add toString() impl to Stat, ignore maven/IDE artifacts

1. Stat.toString() now prints mode in a familiar, readable, form ("drwxrwxrwx"). since IDEs (at least the one im working with?) display toString() return values during debug this becomes very useful. there shouldnt be any effect on production code (as it shouldnt call toString()).

2. added .gitignore for maven /target directories and intellij idea project directories.