Version 1.3.0

Version 1.3.0 adds the following bugfixes and features:

• Remove python-xlib dependency by getting the socket path from i3
  binary.
• The Con::command_children() method should work properly.
• Make socket.recv() robust against interruptions.
• Change Con::mark to Con::marks for the new ipc api (might be
  breaking).
• Add Con::window_rect and Con::deco_rect properties.
• Fix encoding problems in reading README.
• Con::workspace() returns self if it is a workspace instead of None.
• Fix the ipc-shutdown event.
• The library is now installed as a directory instead of a single file.
• Make the main loop work in multi-threaded environments.
• Add Travis CI.
• Add a test suite.
• Add robustness against UTF-8 errors by replacing bad UTF-8.