Merge pull request pytorch#13 from SeanNaren/master

Added FFI build call

Author: soumith

Creating Extensions using FFI.md

@@ -48,12 +48,13 @@ Now, you'll need a super short file, that will build your custom extension:
 ```python
 # build.py
 from torch.utils.ffi import create_extension
-create_extension(
+ffi = create_extension(
 name='_ext.my_lib',
 headers='src/my_lib.h',
 sources=['src/my_lib.c'],
 with_cuda=False
 )
+ffi.build()
 ```
 
 ## Step 2: Include it in your Python code