Add custom 'install' command class
Add custom 'install' command class

CFFIBuild adds ext_modules late in the configuration phase. However,
distutils default 'install' command also parses setup.py and thus misses
that cffi contains several extension modules rather than being pure. As
a consequence, add a CFFIInstall with a proper finalize_options method
and use it.

bwhmather/cryptography,kimvais/cryptography,Ayrx/cryptography,Hasimir/cryptography,dstufft/cryptography,sholsapp/cryptography,sholsapp/cryptography,Ayrx/cryptography,dstufft/cryptography,bwhmather/cryptography,dstufft/cryptography,sholsapp/cryptography,Ayrx/cryptography,skeuomorf/cryptography,skeuomorf/cryptography,kimvais/cryptography,Ayrx/cryptography,bwhmather/cryptography,Hasimir/cryptography,kimvais/cryptography,kimvais/cryptography,bwhmather/cryptography,dstufft/cryptography,dstufft/cryptography,skeuomorf/cryptography,skeuomorf/cryptography,Hasimir/cryptography,sholsapp/cryptography,Hasimir/cryptography