Cythonize screen.py if cython is available

Author: tarruda

.gitignore

@@ -1,2 +1,4 @@
 *.egg-info/
 __pycache__
+neovim/ui/screen.c
+neovim/ui/screen.so

setup.py

@@ -13,9 +13,18 @@
     # trollius is just a backport of 3.4 asyncio module
     install_requires.append('trollius')
 
+has_cython = False
 if not platform.python_implementation() == 'PyPy':
     # pypy already includes an implementation of the greenlet module
     install_requires.append('greenlet')
+    try:
+        # Cythonizing screen.py to improve scrolling/clearing speed. Maybe the
+        # performance can be improved even further by writing a screen.pxd with
+        # static type information
+        from Cython.Build import cythonize
+        has_cython = True
+    except ImportError:
+        pass
 
 setup(name='neovim',
       version='0.0.25',
@@ -28,6 +37,7 @@
       packages=['neovim', 'neovim.api', 'neovim.msgpack_rpc', 'neovim.ui',
                 '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