remove unused code
use FrameworkVersion from environment
exclude unused libs from pack in Windows
update zlib version
libffi-3.0.9 break Python on 32bit linuxes; upgrading to 3.0.13 which is bundled inside Python
Finished release v2.7.6.13.

* release/v2.7.6.13:
  libffi-3.0.9 break Python on 32bit linuxes; upgrading to 3.0.13 which is bundled inside Python
  update zlib version
  exclude unused libs from pack in Windows
  use FrameworkVersion from environment
  remove unused code