Added punycode conversion placeholders and...

internal functions that provide conversion and tests for those
per #120.
Moved things to subdir and adding functions to convert strings.
Fixed panic calls to be similar to others in library
Updated Punycode funcs

* docstrings
* changes to handling invalid punycode names
* updated tests
Added package header.
Changed label splitting and fixed behavior for final period in names.
Replaced rune(0) to new const
Declared variables prior to entering main conversion loops
Prevented crash on empty string to our funcs +...

* changed encodeBytes to encode and decodeBytes to decode
* fixed few comments
Merge pull request #129 from asergeyev/master

Code for handling unicode/punycode name conversions v2