Tnetstring

* Fix memory leak in tnetstring.pop(); thanks tarvip.
* Fix bug in handling of large integers; thanks gdamjan.

* Easy loading of unicode strings. If you pass an optional "encoding"
argument to load/loads/pop then it will return unicode string objects
rather than byte strings.
* Easy dumping of unicode strings. If you pass an optional "encoding"
argument to dump/dumps then it will write unicode strings in that
encoding.

* Initial version; you might say *everything* has changed.