Bump to version 1.4.0

Version 1.4.0 adds the following bugfixes and features:

* 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()`

setup.py

@@ -9,7 +9,7 @@
 
 setup(
     name='i3ipc',
-    version='1.3.0',
+    version='1.4.0',
     description='An improved Python library for i3wm extensions',
     long_description=long_description,
     url='https://github.com/acrisci/i3ipc-python',