Raise a TranslationError if failing to instantiate an object
Corrected tests on Python 2

Python 2 has an io module, messing with StringIO
Added tox configuration
Updated setup.py file
Added the Apache License header to all files
Config is not a singleton anymore

- Multiple clients/servers can have different configurations
- Still a (shared) default configuration object: jsonrpclib.config.DEFAULT
- Previous API should still work as-is: the new parameters have always been
  added in last position, with the DEFAULT instance by default.
- The version all modified modules has been increased to 0.1.6