Method iso.record() doesn't work if using strings as the path argument in Python 3

[thinkdoggie]

In basic usage, a set of strings can be passed as the path argument for method iso.record(). For example:

iso.record("boot", "grub").children

It works well in Python 2, but in Python 3 a KeyError will always be raised with the same code. This is due to the difference of string types between Python 2 and 3. In Python 2, default string type is same as binary type which can be looked up in path_table directly. However, things changes in Python 3.

It looks more convenient and nature to support both legacy strings and unicode strings in this method. Then, it also helps users to write Python 2-3 compatible code with the isoparser library.

[thinkdoggie]

Pull request #21 implemented a patch to fix this issue.