'Show documentation' shows escape codes incorrectly

If you looking at the `writeln` documentation, you'll notice that the `\n` in `write(args, '\n')` is not shown correctly.

This PR use a regex to transform simple escape codes (`\n`, `\t`, etc), octal (`\nnn`), hexa (`\xNN`) and unicode  (`\uNNNN` and `\UNNNNNNNN`) literals into the right escape codes.