Make several improvements to the CFFI build process.

- Move _build_ffi.py to scripts/build_ffi.py. Do as little in the global
namespace of the script as possible by putting functionality into functions,
including a new main function.
- Improve feature detection by allowing user_settings.h in addition to
options.h. This is particularly useful on Windows.
- Add the windows directory. This contains subdirectories non_fips and
fips_ready, which each have a user_settings.h. The non_fips user_settings.h is
used by the build script to build on Windows with CMake, when not using
USE_LOCAL_WOLFSSL. The fips_ready user_settings.h is an example user_settings.h
that works with our FIPS Ready code and wolfcrypt-py.
- Improve Windows support. This commit modifies the way we build wolfSSL for
wolfcrypt-py on Windows. Instead of using CMake directly, we use it with
user_settings.h. This is typically how Windows users are building wolfSSL, and
it gets around some shortcoming of wolfSSL's CMake support (e.g. not all
required features are supported). Additionally, USE_LOCAL_WOLFSSL now works
properly on Windows. When using USE_LOCAL_WOLFSSL, it should point to a wolfSSL
source code directory. This works for FIPS bundles, too. Finally, for FIPS on
Windows, we only support DLL builds. The CFFI library (.pyd extension) requires
this DLL to work. build_ffi.py detects this scenario and copies the .dll into
the wolfcrypt package directory. I've modified setup.py to distribute the
.dll with the package.
- Add some missing FIPS gates. Testing against FIPS v2 triggered some errors.
Those are fixed in this commit.

Author: haydenroche5

.gitignore

@@ -6,6 +6,7 @@ __pycache__/
 # C extensions
 *.so
 *.a
+*.dll
 wolfcrypt/_ffi.*
 
 # Distribution / packaging

MANIFEST.in

@@ -2,6 +2,10 @@ include LICENSING.rst
 include README.rst
 include ChangeLog.rst
 
+include scripts/build_ffi.py
+include windows/fips_ready/user_settings.h
+include windows/non_fips/user_settings.h
+
 recursive-include tests *
 recursive-include requirements *