setup.py: Add optional GUI dependencies.

Author: fwalch

setup.py

@@ -4,13 +4,18 @@
 from setuptools import setup
 
 install_requires = [
-    'click>=3.0',
     'msgpack-python>=0.4.0',
 ]
+gui_requires = [
+    'click>=3.0',
+    'cairo',
+    'gobject'
+]
 
 if sys.version_info < (3, 4):
     # trollius is just a backport of 3.4 asyncio module
     install_requires.append('trollius')
+    gui_requires.append('futures')
 
 has_cython = False
 if not platform.python_implementation() == 'PyPy':
@@ -37,8 +42,10 @@
                 'neovim.msgpack_rpc.event_loop', 'neovim.plugin'],
       install_requires=install_requires,
       ext_modules=cythonize('neovim/ui/screen.py') if has_cython else None,
-      entry_points='''
-      [console_scripts]
-      pynvim=neovim.ui.cli:main
-      ''',
+      extras_require={
+          'Experimental GTK GUI': gui_requires,
+      },
+      entry_points={
+          'console_scripts': ['pynvim=neovim.ui.cli:main [Experimental GTK GUI]'],
+      },
       zip_safe=False)