I3ipc

* fix bug where floating nodes are not in the tree
* add support for SWAYSOCK and other fixes for sway

* Add container property 'floating'
* Add container property 'focus' (the focus stack)
* Add container info for window gaps
* Use native byte order everywhere
* Add descendents iterator to Con
* Add `Con.find_instanced()`
* Add documentation and tests
* List descendents BFS
* Allow usage from external event loops
* bug: return command result in `Con.command()`

- 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.

- Obey I3SOCK environment variable
- Add Con::find_fullscreen()
- Added properties: `scratchpad_state`, `window_role`
- Con::find_marked() - make pattern optional

And the following bugfixes:
- Fix crash on `barconfig_update` event
- Use underscores to subscribe to `barconfig_update` event
- Correctly put floating nodes in the `floating_nodes` list of the Con

- Use enum-compat instead of enum34
- Safely set window class and instance (fixes crashes for windows with
no class or instance)

- Convert README to rst
- fix con::command() formatting
- fix searches to not crash when windows don't have the searched-for
property
- always set class properties
- get_bar_config() defaults to the first bar id
- add get_bar_config_list()