Fixing fbthrift and folly cython bindings build

Summary:
This diff addresses a collection of issues with our thrift-py3 build story in open source.
- Cython 0.29 bug cython/cython#2985 prevents us from loading the generated binary python extensions. I've tested 0.28.6 and it works perfectly.
- Adds ssl to the extensions (since we need SSLContext in get_client, we must have access to the module)
- No need to special case folly_pic. There is really no easy way to get the python bindings to work without using shared library libfolly.so. So, In our build (logdevice) we will build folly as a shared library, this also reduces the complexity everywhere.
- We also need iobuf as extension for thrift to work, added that to setup.py
- Refactored some of the CMake code that had hardcoded file names to use globbing to future-proof this as much as possible.
- Moved `python/lang/cast.pxd` to match the python module name `folly.cast`, so now it lives in `python/cast.pxd`. This simplifies the globbing as well.
- Moved `setup.py` to live in the `/python` directory.
- Added `*.py` in setup.py to pickup any raw python code (including `__init__.py`)

Reviewed By: yfeldblum

Differential Revision: D18685009

fbshipit-source-id: 749b30942a3e5e9e314b5248cc0aa90c6ac1581f

CMakeLists.txt

@@ -163,7 +163,7 @@ endif(lib_only OR build_all)
 if(thriftpy3)
   find_package(PythonInterp 3.6 REQUIRED)
   find_package(PythonLibs 3 REQUIRED)
-  find_package(Cython 0.29 REQUIRED)
+  find_package(Cython 0.28 REQUIRED)
 endif()
 
 # Add the test dependencies

thrift/lib/cpp2/CMakeLists.txt

@@ -188,7 +188,7 @@ if(thriftpy3)
     PUBLIC
       fizz::fizz
       wangle::wangle
-      Folly::folly_pic
+      Folly::folly
       sodium
       ${LIBGFLAGS_LIBRARY}
   )

thrift/lib/py3/CMakeLists.txt

@@ -68,6 +68,7 @@ set(cpp_tgts
   "thrift/py3/serializer.cpp"
   "thrift/py3/client.cpp"
   "thrift/py3/server.cpp"
+  "thrift/py3/ssl.cpp"
 )
 foreach(_mod ${cpp_tgts})
   get_filename_component(_f ${_mod} NAME_WE)

thrift/lib/py3/setup.py

@@ -44,13 +44,14 @@ def build_extension(self, ext):
     Extension("thrift.py3.serializer", sources=["thrift/py3/serializer.so"]),
     Extension("thrift.py3.client", sources=["thrift/py3/client.so"]),
     Extension("thrift.py3.server", sources=["thrift/py3/server.so"]),
+    Extension("thrift.py3.ssl", sources=["thrift/py3/ssl.so"]),
 ]
 setup(
     name="thrift",
     cmdclass={"build_ext": copy_cmake_built_libs_build_ext},
     version="0.0.1",
     packages=["thrift", "thrift.py3"],
-    package_data={"": ["*.pxd", "*.h", "__init__.pyx"]},
+    package_data={"": ["*.pxd", "*.h", "__init__.pyx", "*.py"]},
     zip_safe=False,
     ext_modules=extensions,
 )